Publications
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2021 |
Pengshang Zhou Pieter Schiettecatte, Matthias Vandichel Anastasia Rousaki Peter Vandenabeele Zeger Hens ; Singh*, Shalini Synthesis of Colloidal WSe2 Nanocrystals: Polymorphism Control by Precursor-Ligand Chemistry Journal Article Forthcoming Crystal Growth & Design, Forthcoming. @article{Zhou2021, title = {Synthesis of Colloidal WSe2 Nanocrystals: Polymorphism Control by Precursor-Ligand Chemistry}, author = {Pengshang Zhou, Pieter Schiettecatte, Matthias Vandichel, Anastasia Rousaki, Peter Vandenabeele, Zeger Hens, and Shalini Singh*}, doi = {https://doi.org/10.1021/acs.cgd.0c01036}, year = {2021}, date = {2021-01-29}, journal = {Crystal Growth & Design}, abstract = {Syntheses of transition-metal dichalcogenides (TMDs) using colloidal-chemistry approaches are gaining significant interest in recent years, as these methods enable the morphology and properties of the nanocrystals to be tuned for targeted applications. In this work, by only varying the ligand used during synthesis, we synthesized nanoflowers with oleic acid (OA) and 1T′ phase dominated WSe2 nanosheets with oleylamine (OLA). WSe2 nanocrystals show slower rate of formation for the metastable 1T′ phase. Surface chemistry analyses of the synthesized nanocrystals by solution NMR establish that neither of the ligands bind strongly to the surface of nanocrystals but are in a dynamic coordination with the WSe2 surface. A further examination of the coordination of tungsten hexacarbonyl (W(CO)6) with the respective ligands confirms that W(CO)6 decomposes in OA, losing its octahedral symmetry, which leads to fast reactivity in the flask. In contrast to this, W(CO)6 reacts with OLA to form a new complex, which leads to slower reactivity and crystallization of the synthesized nanocrystals in the octahedral 1T′ phase. These insights into the influence of precursor-ligand chemistry on reaction outcome and the peculiar surface chemistry of colloidal TMD nanocrystals will be instrumental in developing future colloidal TMD nanocrystals.}, keywords = {}, pubstate = {forthcoming}, tppubtype = {article} } Syntheses of transition-metal dichalcogenides (TMDs) using colloidal-chemistry approaches are gaining significant interest in recent years, as these methods enable the morphology and properties of the nanocrystals to be tuned for targeted applications. In this work, by only varying the ligand used during synthesis, we synthesized nanoflowers with oleic acid (OA) and 1T′ phase dominated WSe2 nanosheets with oleylamine (OLA). WSe2 nanocrystals show slower rate of formation for the metastable 1T′ phase. Surface chemistry analyses of the synthesized nanocrystals by solution NMR establish that neither of the ligands bind strongly to the surface of nanocrystals but are in a dynamic coordination with the WSe2 surface. A further examination of the coordination of tungsten hexacarbonyl (W(CO)6) with the respective ligands confirms that W(CO)6 decomposes in OA, losing its octahedral symmetry, which leads to fast reactivity in the flask. In contrast to this, W(CO)6 reacts with OLA to form a new complex, which leads to slower reactivity and crystallization of the synthesized nanocrystals in the octahedral 1T′ phase. These insights into the influence of precursor-ligand chemistry on reaction outcome and the peculiar surface chemistry of colloidal TMD nanocrystals will be instrumental in developing future colloidal TMD nanocrystals. |
2020 |
Vandichel, Matthias; Laasonen, Kari; Kondov, Ivan Oxygen Evolution and Reduction on Fe-doped NiOOH: Influence of Solvent, Dopant Position and Reaction Mechanism Journal Article TOPICS IN CATALYSIS, 2020, ISSN: 1022-5528. @article{ISI:000553709000001, title = {Oxygen Evolution and Reduction on Fe-doped NiOOH: Influence of Solvent, Dopant Position and Reaction Mechanism}, author = {Matthias Vandichel and Kari Laasonen and Ivan Kondov}, url = {https://doi.org/10.1007/s11244-020-01334-8}, doi = {10.1007/s11244-020-01334-8}, issn = {1022-5528}, year = {2020}, date = {2020-07-29}, journal = {TOPICS IN CATALYSIS}, abstract = {The oxygen evolution reaction (OER) is the limiting factor in an electrolyzer and the oxygen reduction reaction (ORR) the limiting factor in a fuel cell. In OER, water is converted to O(2)and H+/e(-)pairs, while in ORR the reverse process happens to form water. Both reactions and their efficiency are important enablers of a hydrogen economy where hydrogen will act as a fuel or energy storage medium. OER and ORR can both be described assuming a four-step electrochemical mechanism with coupled H+/e(-)transfers between four intermediates (M-*}, keywords = {}, pubstate = {published}, tppubtype = {article} } The oxygen evolution reaction (OER) is the limiting factor in an electrolyzer and the oxygen reduction reaction (ORR) the limiting factor in a fuel cell. In OER, water is converted to O(2)and H+/e(-)pairs, while in ORR the reverse process happens to form water. Both reactions and their efficiency are important enablers of a hydrogen economy where hydrogen will act as a fuel or energy storage medium. OER and ORR can both be described assuming a four-step electrochemical mechanism with coupled H+/e(-)transfers between four intermediates (M-* |
Younus, Hussein A; Zhang, Yan; Vandichel, Matthias; Ahmad, Nazir; Laasonen, Kari; Verpoort, Francis; Zhang, Ce; Zhang, Shiguo Water Oxidation at Neutral pH using a Highly Active Copper-Based Electrocatalyst Journal Article CHEMSUSCHEM, 2020, ISSN: 1864-5631. @article{ISI:000557552100001, title = {Water Oxidation at Neutral pH using a Highly Active Copper-Based Electrocatalyst}, author = {Hussein A Younus and Yan Zhang and Matthias Vandichel and Nazir Ahmad and Kari Laasonen and Francis Verpoort and Ce Zhang and Shiguo Zhang}, doi = {10.1002/cssc.202001444}, issn = {1864-5631}, year = {2020}, date = {2020-07-15}, journal = {CHEMSUSCHEM}, abstract = {The sluggish kinetics of the oxygen evolution reaction (OER) at the anode severely limit hydrogen production at the cathode in water splitting systems. Although electrocatalytic systems based on cheap and earth-abundant copper catalysts have shown promise for water oxidation under basic conditions, only very few examples with high overpotential can be operated under acidic or neutral conditions, even though hydrogen evolution in the latter case is much easier. This work presents an efficient and robust Cu-based molecular catalyst, which self-assembles as a periodic film from its precursors under aqueous conditions on the surface of a glassy carbon electrode. This film catalyzes the OER under neutral conditions with impressively low overpotential. In controlled potential electrolysis, a stable catalytic current of 1.0 mA cm(-2)can be achieved at only 2.0 V (vs. RHE) and no significant decrease in the catalytic current is observed even after prolonged bulk electrolysis. The catalyst displays first-order kinetics and a single site mechanism for water oxidation with a TOF (k(cat)) of 0.6 s(-1). DFT calculations on of the periodic Cu(TCA)(2)(HTCA=1-mesityl-1H-1,2,3-triazole-4-carboxylic acid) film reveal that TCA defects within the film create Cu(I)active sites that provide a low overpotential route for OER, which involves Cu-I, Cu-II-OH}, keywords = {}, pubstate = {published}, tppubtype = {article} } The sluggish kinetics of the oxygen evolution reaction (OER) at the anode severely limit hydrogen production at the cathode in water splitting systems. Although electrocatalytic systems based on cheap and earth-abundant copper catalysts have shown promise for water oxidation under basic conditions, only very few examples with high overpotential can be operated under acidic or neutral conditions, even though hydrogen evolution in the latter case is much easier. This work presents an efficient and robust Cu-based molecular catalyst, which self-assembles as a periodic film from its precursors under aqueous conditions on the surface of a glassy carbon electrode. This film catalyzes the OER under neutral conditions with impressively low overpotential. In controlled potential electrolysis, a stable catalytic current of 1.0 mA cm(-2)can be achieved at only 2.0 V (vs. RHE) and no significant decrease in the catalytic current is observed even after prolonged bulk electrolysis. The catalyst displays first-order kinetics and a single site mechanism for water oxidation with a TOF (k(cat)) of 0.6 s(-1). DFT calculations on of the periodic Cu(TCA)(2)(HTCA=1-mesityl-1H-1,2,3-triazole-4-carboxylic acid) film reveal that TCA defects within the film create Cu(I)active sites that provide a low overpotential route for OER, which involves Cu-I, Cu-II-OH |
Braglia, Luca; Fracchia, Martina; Ghigna, Paolo; Minguzzi, Alessandro; Meroni, Daniela; Edla, Raju; Vandichel, Matthias; Ahlberg, Elisabet; Cerrato, Giuseppina; Torelli, Piero Understanding Solid-Gas Reaction Mechanisms by Operando Soft X-Ray Absorption Spectroscopy at Ambient Pressure Journal Article JOURNAL OF PHYSICAL CHEMISTRY C, 124 (26), pp. 14202-14212, 2020, ISSN: 1932-7447. @article{ISI:000547455300015, title = {Understanding Solid-Gas Reaction Mechanisms by Operando Soft X-Ray Absorption Spectroscopy at Ambient Pressure}, author = {Luca Braglia and Martina Fracchia and Paolo Ghigna and Alessandro Minguzzi and Daniela Meroni and Raju Edla and Matthias Vandichel and Elisabet Ahlberg and Giuseppina Cerrato and Piero Torelli}, doi = {10.1021/acs.jpcc.0c02546}, issn = {1932-7447}, year = {2020}, date = {2020-07-01}, journal = {JOURNAL OF PHYSICAL CHEMISTRY C}, volume = {124}, number = {26}, pages = {14202-14212}, abstract = {Ambient-pressure operando soft X-ray absorption spectroscopy (soft-XAS) was applied to study the reactivity of hydroxylated SnO(2 )nanoparticles toward reducing gases. H-2 was first used as a test case, showing that the gas phase and surface states can be simultaneously probed: Soft-XAS at the O K-edge gains sensitivity toward the gas phase, while at the Sn M-4,M-5-edges, tin surface states are explicitly probed. Results obtained by flowing hydrocarbons (CH4 and CH3CHCH2) unequivocally show that these gases react with surface hydroxyl groups to produce water without producing carbon oxides and release electrons that localize on Sn to eventually form SnO. The partially reduced SnO2-x layer at the surface of SnO2 is readily reoxidized to SnO2 by treating the sample with O-2 at mild temperatures (>200 degrees C), revealing the nature of ``electron sponge'' of tin oxide. The experiments, combined with DFT calculations, allowed devising of a mechanism for dissociative hydrocarbon adsorption on SnO2, involving direct reduction of Sn sites at the surface via cleavage of C-H bonds and the formation of methoxy- and/or methyl-tin species at the surface.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Ambient-pressure operando soft X-ray absorption spectroscopy (soft-XAS) was applied to study the reactivity of hydroxylated SnO(2 )nanoparticles toward reducing gases. H-2 was first used as a test case, showing that the gas phase and surface states can be simultaneously probed: Soft-XAS at the O K-edge gains sensitivity toward the gas phase, while at the Sn M-4,M-5-edges, tin surface states are explicitly probed. Results obtained by flowing hydrocarbons (CH4 and CH3CHCH2) unequivocally show that these gases react with surface hydroxyl groups to produce water without producing carbon oxides and release electrons that localize on Sn to eventually form SnO. The partially reduced SnO2-x layer at the surface of SnO2 is readily reoxidized to SnO2 by treating the sample with O-2 at mild temperatures (>200 degrees C), revealing the nature of ``electron sponge'' of tin oxide. The experiments, combined with DFT calculations, allowed devising of a mechanism for dissociative hydrocarbon adsorption on SnO2, involving direct reduction of Sn sites at the surface via cleavage of C-H bonds and the formation of methoxy- and/or methyl-tin species at the surface. |
Song, Bai-Qiao; Yang, Qing-Yuan; Wang, Shi-Qiang; Vandichel, Matthias; Kumar, Amrit; Crowley, Clare; Kumar, Naveen; Deng, Cheng-Hua; GasconPerez, Victoria; Lusi, Matteo; Wu, Hui; Zhou, Wei; Zaworotko, Michael J Reversible Switching between Nonporous and Porous Phases of a New SIFSIX Coordination Network Induced by a Flexible Linker Ligand Journal Article JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 142 (15), pp. 6896-6901, 2020, ISSN: 0002-7863. @article{ISI:000526300600012, title = {Reversible Switching between Nonporous and Porous Phases of a New SIFSIX Coordination Network Induced by a Flexible Linker Ligand}, author = {Bai-Qiao Song and Qing-Yuan Yang and Shi-Qiang Wang and Matthias Vandichel and Amrit Kumar and Clare Crowley and Naveen Kumar and Cheng-Hua Deng and Victoria GasconPerez and Matteo Lusi and Hui Wu and Wei Zhou and Michael J Zaworotko}, doi = {10.1021/jacs.0c01314}, issn = {0002-7863}, year = {2020}, date = {2020-04-01}, journal = {JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, volume = {142}, number = {15}, pages = {6896-6901}, abstract = {Closed-to-open structural transformations in flexible coordination networks are of potential utility in gas storage and separation. Herein, we report the first example of a flexible SiF62--pillared square grid material, [Cu(SiF6)(L)(2)](n) (L = 1,4-bis(1-imidazolyl)benzene), SIFSIX-23-Cu. SIFSIX-23-Cu exhibits reversible switching between nonporous (beta 1) and several porous (alpha, gamma 1, gamma 2, and gamma 3) phases triggered by exposure to N-2, CO2, or H2O. In addition, heating beta 1 to 433 K resulted in irreversible transformation to a closed polymorph, beta 2. Single-crystal X-ray diffraction studies revealed that the phase transformations are enabled by rotation and geometrical contortion of L. Density functional theory calculations indicated that L exhibits a low barrier to rotation (as low as 8 kJmol(-1)) and a rather flat energy surface. In situ neutron powder diffraction studies provided further insight into these sorbate-induced phase changes. SIFSIX-23-Cu combines stability in water for over a year, high CO2 uptake (ca. 216 cm(3)/g at 195 K), and good thermal stability.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Closed-to-open structural transformations in flexible coordination networks are of potential utility in gas storage and separation. Herein, we report the first example of a flexible SiF62--pillared square grid material, [Cu(SiF6)(L)(2)](n) (L = 1,4-bis(1-imidazolyl)benzene), SIFSIX-23-Cu. SIFSIX-23-Cu exhibits reversible switching between nonporous (beta 1) and several porous (alpha, gamma 1, gamma 2, and gamma 3) phases triggered by exposure to N-2, CO2, or H2O. In addition, heating beta 1 to 433 K resulted in irreversible transformation to a closed polymorph, beta 2. Single-crystal X-ray diffraction studies revealed that the phase transformations are enabled by rotation and geometrical contortion of L. Density functional theory calculations indicated that L exhibits a low barrier to rotation (as low as 8 kJmol(-1)) and a rather flat energy surface. In situ neutron powder diffraction studies provided further insight into these sorbate-induced phase changes. SIFSIX-23-Cu combines stability in water for over a year, high CO2 uptake (ca. 216 cm(3)/g at 195 K), and good thermal stability. |
Vandichel, Matthias; Busch, Michael; Laasonen, Kari Oxygen Evolution on Metal-oxy-hydroxides: Beneficial Role of Mixing Fe, Co, Ni Explained via Bifunctional Edge/acceptor Route Journal Article CHEMCATCHEM, 12 (5), pp. 1436-1442, 2020, ISSN: 1867-3880. @article{ISI:000505822700001, title = {Oxygen Evolution on Metal-oxy-hydroxides: Beneficial Role of Mixing Fe, Co, Ni Explained via Bifunctional Edge/acceptor Route}, author = {Matthias Vandichel and Michael Busch and Kari Laasonen}, doi = {10.1002/cctc.201901951}, issn = {1867-3880}, year = {2020}, date = {2020-03-01}, journal = {CHEMCATCHEM}, volume = {12}, number = {5}, pages = {1436-1442}, abstract = {Oxygen evolution reaction (OER) via mixed metal oxy hydroxides [M(O)(OH)] may take place on a large variety of possible active sites on the actual catalyst. A single site computational description assumes a 4-step electrochemical mechanism with coupled H+/e(-) transfers between 4 intermediates (M-*, M-OH}, keywords = {}, pubstate = {published}, tppubtype = {article} } Oxygen evolution reaction (OER) via mixed metal oxy hydroxides [M(O)(OH)] may take place on a large variety of possible active sites on the actual catalyst. A single site computational description assumes a 4-step electrochemical mechanism with coupled H+/e(-) transfers between 4 intermediates (M-*, M-OH |
Younus, H A; Vandichel, M; Ahmad, N; Ahlberg, E; Busch, M; Verpoort, F Engineering of a highly stable metal-organic Co-film for efficient electrocatalytic water oxidation in acidic media Journal Article Materials Today Energy, 17 , pp. 100437, 2020, ISSN: 2468-6069. @article{YOUNUS2020100437, title = {Engineering of a highly stable metal-organic Co-film for efficient electrocatalytic water oxidation in acidic media}, author = {H A Younus and M Vandichel and N Ahmad and E Ahlberg and M Busch and F Verpoort}, url = {http://www.sciencedirect.com/science/article/pii/S2468606920300563}, doi = {10.1016/j.mtener.2020.100437}, issn = {2468-6069}, year = {2020}, date = {2020-01-01}, journal = {Materials Today Energy}, volume = {17}, pages = {100437}, abstract = {Water oxidation is traditionally performed over IrO2 and RuO2 owing to their high stability at low pH compared to molecular O2 evolution catalysts. The low stability of molecular complexes in acids limits their industrial exploitation as anodes in water-splitting devices, where high current densities and proton conductivity are required. Herein, an existing Co(1,10-phenanthroline)2 complex film is engineered to improve its pH-stability via extra OH substituents on the ligand, i.e. 1,10-phenanthroline-4,7-diol. This novel Co(1,10-phenanthroline-4,7-diol)2 complex film is active for water oxidation at low overpotentials and stable at low pH. Since the calculated water oxidation overpotentials of both complexes are similar, the difference in water oxidation activity is attributed to a smaller charge transfer resistance, which originates from a different anchoring style to the electrode via the OH groups of the ligand. This result is supported by electrochemical impedance measurements. The high pH-stability of the Co(1,10-phenanthroline-4,7-diol)2 film is computationally rationalized by a high crystal formation energy observed in DFT calculations. In summary, an acid-stable and active cobalt-based metal-organic film is reported that competes well with most reported earth-abundant catalysts for water oxidation under similar conditions.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Water oxidation is traditionally performed over IrO2 and RuO2 owing to their high stability at low pH compared to molecular O2 evolution catalysts. The low stability of molecular complexes in acids limits their industrial exploitation as anodes in water-splitting devices, where high current densities and proton conductivity are required. Herein, an existing Co(1,10-phenanthroline)2 complex film is engineered to improve its pH-stability via extra OH substituents on the ligand, i.e. 1,10-phenanthroline-4,7-diol. This novel Co(1,10-phenanthroline-4,7-diol)2 complex film is active for water oxidation at low overpotentials and stable at low pH. Since the calculated water oxidation overpotentials of both complexes are similar, the difference in water oxidation activity is attributed to a smaller charge transfer resistance, which originates from a different anchoring style to the electrode via the OH groups of the ligand. This result is supported by electrochemical impedance measurements. The high pH-stability of the Co(1,10-phenanthroline-4,7-diol)2 film is computationally rationalized by a high crystal formation energy observed in DFT calculations. In summary, an acid-stable and active cobalt-based metal-organic film is reported that competes well with most reported earth-abundant catalysts for water oxidation under similar conditions. |
Dhokale, Bhausaheb; Susarrey-Arce, Arturo; Pekkari, Anna; Runemark, August; Moth-Poulsen, Kasper; Langhammer, Christoph; Härelind, Hanna; Busch, Michael; Vandichel, Matthias; Sundén, Henrik Microwave-heated γ-Alumina Applied to the Reduction of Aldehydes to Alcohols Journal Article ChemCatChem, 12 (24), pp. 6344-6355, 2020. @article{https://doi.org/10.1002/cctc.202001284, title = {Microwave-heated γ-Alumina Applied to the Reduction of Aldehydes to Alcohols}, author = {Bhausaheb Dhokale and Arturo Susarrey-Arce and Anna Pekkari and August Runemark and Kasper Moth-Poulsen and Christoph Langhammer and Hanna Härelind and Michael Busch and Matthias Vandichel and Henrik Sundén}, url = {https://chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/cctc.202001284}, doi = {https://doi.org/10.1002/cctc.202001284}, year = {2020}, date = {2020-01-01}, journal = {ChemCatChem}, volume = {12}, number = {24}, pages = {6344-6355}, abstract = {Abstract The development of cheap and robust heterogeneous catalysts for the Meerwein-Ponndorf-Verley (MPV) reduction is desirable due to the difficulties in product isolation and catalyst recovery associated with the traditional use of homogeneous catalysts for MPV. Herein, we show that microwave heated γ-Al2O3 can be used for the reduction of aldehydes to alcohols. The reaction is efficient and has a broad substrates scope (19 entries). The products can be isolated by simple filtration, and the catalyst can be regenerated. With the use of microwave heating, we can direct the heating to the catalyst rather than to the whole reaction medium. Furthermore, DFT was used to study the reaction mechanism, and we can conclude that a dual-site mechanism is operative where the aldehyde and 2-propoxide are situated on two adjacent Al sites during the reduction. Additionally, volcano plots were used to rationalize the reactivity of Al2O3 in comparison to other metal oxides.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Abstract The development of cheap and robust heterogeneous catalysts for the Meerwein-Ponndorf-Verley (MPV) reduction is desirable due to the difficulties in product isolation and catalyst recovery associated with the traditional use of homogeneous catalysts for MPV. Herein, we show that microwave heated γ-Al2O3 can be used for the reduction of aldehydes to alcohols. The reaction is efficient and has a broad substrates scope (19 entries). The products can be isolated by simple filtration, and the catalyst can be regenerated. With the use of microwave heating, we can direct the heating to the catalyst rather than to the whole reaction medium. Furthermore, DFT was used to study the reaction mechanism, and we can conclude that a dual-site mechanism is operative where the aldehyde and 2-propoxide are situated on two adjacent Al sites during the reduction. Additionally, volcano plots were used to rationalize the reactivity of Al2O3 in comparison to other metal oxides. |
Kumar, Naveen; Mukherjee, Soumya; Bezrukov, Andrey A; Vandichel, Matthias; Shivanna, Mohana; Sensharma, Debobroto; Bajpai, Alankriti; Gascón, Victoria; Otake, Ken-ichi; Kitagawa, Susumu; Zaworotko, Michael J A square lattice topology coordination network that exhibits highly selective C2H2/CO2 separation performance Journal Article SmartMat, 1 (1), pp. e1008, 2020. @article{https://doi.org/10.1002/smm2.1008, title = {A square lattice topology coordination network that exhibits highly selective C2H2/CO2 separation performance}, author = {Naveen Kumar and Soumya Mukherjee and Andrey A Bezrukov and Matthias Vandichel and Mohana Shivanna and Debobroto Sensharma and Alankriti Bajpai and Victoria Gascón and Ken-ichi Otake and Susumu Kitagawa and Michael J Zaworotko}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/smm2.1008}, doi = {https://doi.org/10.1002/smm2.1008}, year = {2020}, date = {2020-01-01}, journal = {SmartMat}, volume = {1}, number = {1}, pages = {e1008}, abstract = {Abstract C2H2/CO2 separation is an industrially important process that remains challenging because of the similar physicochemical properties of C2H2 and CO2. We herein report that the new square lattice (sql) coordination network [Cu(bipy-xylene)2(NO3)2]n, sql-16-Cu-NO3, 16 = bipy-xylene = 4,4′-(2,5-dimethyl-1,4-phenylene)dipyridine, exists in at least three forms, as-synthesised (α), activated (α′) and hydrated (β). The activated phase, sql-16-Cu-NO3-α′, is an ultramicroporous material that exhibits high selectivity towards C2H2 over CO2 as revealed by dynamic gas breakthrough experiments (1:1, C2H2/CO2) that afforded 99.87% pure CO2 in the effluent stream. The separation selectivity at 298 K and 1 bar, 78, is the third best value yet reported for C2H2 selective physisorbents whereas the mid-loading performance sets a new benchmark. The performance of sql-16-Cu-NO3-α′ is attributed to a new type of C2H2 binding site in which CH···ONO2 interactions enable moderately strong sorbent-sorbate binding (Qst (C2H2) = 38.6 kJ/mol) at low loading. Conversely, weak CO2 binding (Qst (CO2) = 25.6 kJ/mol) at low loading means that (ΔQst)AC [Qst (C2H2)–Qst (CO2)] is 13 kJ/mol at low coverage and 11.4 kJ/mol at mid-loading. Analysis of in situ powder X-ray diffraction and modelling experiments provide insight into the sorption properties and high C2H2/CO2 separation performance of sql-16-Cu-NO3-α′.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Abstract C2H2/CO2 separation is an industrially important process that remains challenging because of the similar physicochemical properties of C2H2 and CO2. We herein report that the new square lattice (sql) coordination network [Cu(bipy-xylene)2(NO3)2]n, sql-16-Cu-NO3, 16 = bipy-xylene = 4,4′-(2,5-dimethyl-1,4-phenylene)dipyridine, exists in at least three forms, as-synthesised (α), activated (α′) and hydrated (β). The activated phase, sql-16-Cu-NO3-α′, is an ultramicroporous material that exhibits high selectivity towards C2H2 over CO2 as revealed by dynamic gas breakthrough experiments (1:1, C2H2/CO2) that afforded 99.87% pure CO2 in the effluent stream. The separation selectivity at 298 K and 1 bar, 78, is the third best value yet reported for C2H2 selective physisorbents whereas the mid-loading performance sets a new benchmark. The performance of sql-16-Cu-NO3-α′ is attributed to a new type of C2H2 binding site in which CH···ONO2 interactions enable moderately strong sorbent-sorbate binding (Qst (C2H2) = 38.6 kJ/mol) at low loading. Conversely, weak CO2 binding (Qst (CO2) = 25.6 kJ/mol) at low loading means that (ΔQst)AC [Qst (C2H2)–Qst (CO2)] is 13 kJ/mol at low coverage and 11.4 kJ/mol at mid-loading. Analysis of in situ powder X-ray diffraction and modelling experiments provide insight into the sorption properties and high C2H2/CO2 separation performance of sql-16-Cu-NO3-α′. |
2019 |
Belviso, Florian; Claerbout, Victor E P; Comas-Vives, Aleix; Dalal, Naresh S; Fan, Feng-Ren; Filippetti, Alessio; Fiorentini, Vincenzo; Foppa, Lucas; Franchini, Cesare; Geisler, Benjamin; Ghiringhelli, Luca M; Gross, Axel; Hu, Shunbo; Iniguez, Jorge; Kauwe, Steven Kaai; Musfeldt, Janice L; Nicolini, Paolo; Pentcheva, Rossitza; Polcar, Tomas; Ren, Wei; Ricci, Fabio; Ricci, Francesco; Sen, Huseyin Sener; Skelton, Jonathan Michael; Sparks, Taylor D; Stroppa, Alessandro; Urru, Andrea; Vandichel, Matthias; Vavassori, Paolo; Wu, Hua; Yang, Ke; Zhao, Hong Jian; Puggioni, Danilo; Cortese, Remedios; Cammarata, Antonio Viewpoint: Atomic-Scale Design Protocols toward Energy, Electronic, Catalysis, and Sensing Applications Journal Article INORGANIC CHEMISTRY, 58 (22), pp. 14939-14980, 2019, ISSN: 0020-1669. @article{ISI:000498288300001, title = {Viewpoint: Atomic-Scale Design Protocols toward Energy, Electronic, Catalysis, and Sensing Applications}, author = {Florian Belviso and Victor E P Claerbout and Aleix Comas-Vives and Naresh S Dalal and Feng-Ren Fan and Alessio Filippetti and Vincenzo Fiorentini and Lucas Foppa and Cesare Franchini and Benjamin Geisler and Luca M Ghiringhelli and Axel Gross and Shunbo Hu and Jorge Iniguez and Steven Kaai Kauwe and Janice L Musfeldt and Paolo Nicolini and Rossitza Pentcheva and Tomas Polcar and Wei Ren and Fabio Ricci and Francesco Ricci and Huseyin Sener Sen and Jonathan Michael Skelton and Taylor D Sparks and Alessandro Stroppa and Andrea Urru and Matthias Vandichel and Paolo Vavassori and Hua Wu and Ke Yang and Hong Jian Zhao and Danilo Puggioni and Remedios Cortese and Antonio Cammarata}, doi = {10.1021/acs.inorgchem.9b01785}, issn = {0020-1669}, year = {2019}, date = {2019-11-01}, journal = {INORGANIC CHEMISTRY}, volume = {58}, number = {22}, pages = {14939-14980}, abstract = {Nanostructured materials are essential building blocks for the fabrication of new devices for energy harvesting/storage, sensing, catalysis, magnetic, and optoelectronic applications. However, because of the increase of technological needs, it is essential to identify new functional materials and improve the properties of existing ones. The objective of this Viewpoint is to examine the state of the art of atomic-scale simulative and experimental protocols aimed to the design of novel functional nanostructured materials, and to present new perspectives in the relative fields. This is the result of the debates of Symposium I ``Atomic-scale design protocols towards energy, electronic, catalysis, and sensing applications'', which took place within the 2018 European Materials Research Society fall meeting.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Nanostructured materials are essential building blocks for the fabrication of new devices for energy harvesting/storage, sensing, catalysis, magnetic, and optoelectronic applications. However, because of the increase of technological needs, it is essential to identify new functional materials and improve the properties of existing ones. The objective of this Viewpoint is to examine the state of the art of atomic-scale simulative and experimental protocols aimed to the design of novel functional nanostructured materials, and to present new perspectives in the relative fields. This is the result of the debates of Symposium I ``Atomic-scale design protocols towards energy, electronic, catalysis, and sensing applications'', which took place within the 2018 European Materials Research Society fall meeting. |
Soldemo, Markus; Vandichel, Matthias; Gronbeck, Henrik; Weissenrieder, Jonas Initial Fe3O4(100) Formation on Fe(100) Journal Article JOURNAL OF PHYSICAL CHEMISTRY C, 123 (26), pp. 16317-16325, 2019, ISSN: 1932-7447. @article{ISI:000474796600046, title = {Initial Fe3O4(100) Formation on Fe(100)}, author = {Markus Soldemo and Matthias Vandichel and Henrik Gronbeck and Jonas Weissenrieder}, doi = {10.1021/acs.jpcc.9b04625}, issn = {1932-7447}, year = {2019}, date = {2019-07-01}, journal = {JOURNAL OF PHYSICAL CHEMISTRY C}, volume = {123}, number = {26}, pages = {16317-16325}, abstract = {The initial oxidation of Fe(100) at 400 degrees C has been studied by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and low-energy electron diffraction, in combination with density functional theory calculations. The first observed well-ordered surface oxide is formed at a coverage of similar to 3 oxygen atoms per unreconstructed surface Fe(100) atom. STM shows that this surface oxide is terminated by straight atomic rows exhibiting a p(2 X 1) periodicity. However, already for oxide films with a coverage of similar to 4 oxygen atoms (corresponding to one Fe3O4 unit cell thickness), wiggly atomic rows appear similar to the c(2 X 2) reconstructed Fe3O4 (100)-surface with the Fe3O4 unit vectors rotated 45 degrees to Fe(100). The wiggly rows are a consequence of subsurface cation iron vacancies, which previously have been observed for bulk surfaces. The formation of subsurface vacancies is supported by the XPS O is signature, which is modeled by considering the core-level shifts for all oxygen atoms in the film. Throughout the oxidation series, the microscopy results reveal a layer-by-layer (Frank-van der Merwe) growth.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The initial oxidation of Fe(100) at 400 degrees C has been studied by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and low-energy electron diffraction, in combination with density functional theory calculations. The first observed well-ordered surface oxide is formed at a coverage of similar to 3 oxygen atoms per unreconstructed surface Fe(100) atom. STM shows that this surface oxide is terminated by straight atomic rows exhibiting a p(2 X 1) periodicity. However, already for oxide films with a coverage of similar to 4 oxygen atoms (corresponding to one Fe3O4 unit cell thickness), wiggly atomic rows appear similar to the c(2 X 2) reconstructed Fe3O4 (100)-surface with the Fe3O4 unit vectors rotated 45 degrees to Fe(100). The wiggly rows are a consequence of subsurface cation iron vacancies, which previously have been observed for bulk surfaces. The formation of subsurface vacancies is supported by the XPS O is signature, which is modeled by considering the core-level shifts for all oxygen atoms in the film. Throughout the oxidation series, the microscopy results reveal a layer-by-layer (Frank-van der Merwe) growth. |
Vandichel, Matthias; Gronbeck, Henrik A dimer path for CO dissociation on PtSn Journal Article CATALYSIS SCIENCE & TECHNOLOGY, 9 (3), pp. 695-701, 2019, ISSN: 2044-4753. @article{ISI:000459731200013, title = {A dimer path for CO dissociation on PtSn}, author = {Matthias Vandichel and Henrik Gronbeck}, doi = {10.1039/c8cy01989d}, issn = {2044-4753}, year = {2019}, date = {2019-02-01}, journal = {CATALYSIS SCIENCE & TECHNOLOGY}, volume = {9}, number = {3}, pages = {695-701}, abstract = {Density functional theory calculations are used to investigate CO adsorption, dissociation and SnOX formation on Pt3Sn. We find that direct CO dissociation is prevented by high activation energies. An energetically feasible path is instead CO dimer formation followed by C-O bond cleavage. Dimers are formed in the presence of Sn adatoms which effectively stabilize anionic OCCO- species. The presence of Sn adatoms is crucial as dimers are unstable on Pt-only systems. The proposed mechanism may explain recent experimental observations of SnOX and C-C formation as PtxSn is exposed to CO.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Density functional theory calculations are used to investigate CO adsorption, dissociation and SnOX formation on Pt3Sn. We find that direct CO dissociation is prevented by high activation energies. An energetically feasible path is instead CO dimer formation followed by C-O bond cleavage. Dimers are formed in the presence of Sn adatoms which effectively stabilize anionic OCCO- species. The presence of Sn adatoms is crucial as dimers are unstable on Pt-only systems. The proposed mechanism may explain recent experimental observations of SnOX and C-C formation as PtxSn is exposed to CO. |
2018 |
Vandichel, Matthias; Gronbeck, Henrik CO Oxidation at SnO2/Pt3Sn(111) Interfaces Journal Article TOPICS IN CATALYSIS, 61 (14, SI), pp. 1458-1464, 2018, ISSN: 1022-5528, (13th European Congress on Catalysis - A Bridge to the Future, Florence, ITALY, AUG 27-31, 2017). @article{ISI:000445805100009, title = {CO Oxidation at SnO2/Pt3Sn(111) Interfaces}, author = {Matthias Vandichel and Henrik Gronbeck}, doi = {10.1007/s11244-018-1044-9}, issn = {1022-5528}, year = {2018}, date = {2018-09-01}, journal = {TOPICS IN CATALYSIS}, volume = {61}, number = {14, SI}, pages = {1458-1464}, abstract = {Segregation induced formation of oxide/metal interfaces can significantly influence the catalytic activity of alloy nanoparticles. One example is Pt3Sn nanoparticles, which are known to segregate into SnOX and an Sn deficient alloy phase during typical operating conditions for CO oxidation. Here, we use density functional theory calculations to investigate CO oxidation over Pt3Sn(111) supported SnO2 and (SnO2)(3), representing the initial state of segregation. The results are compared to CO oxidation at an interface between bulk-like SnO2 and Pt3Sn(111). The barrier for CO oxidation via a Mars-van Krevelen mechanism is found to be lower on SnO2 and (SnO2)(3) as compared to the bulk-like model. However, the regeneration of the finite systems is associated with higher barriers for O-2 dissociation which may become the rate limiting step in the low temperature regime where the metal surface can be assumed to be CO covered.}, note = {13th European Congress on Catalysis - A Bridge to the Future, Florence, ITALY, AUG 27-31, 2017}, keywords = {}, pubstate = {published}, tppubtype = {article} } Segregation induced formation of oxide/metal interfaces can significantly influence the catalytic activity of alloy nanoparticles. One example is Pt3Sn nanoparticles, which are known to segregate into SnOX and an Sn deficient alloy phase during typical operating conditions for CO oxidation. Here, we use density functional theory calculations to investigate CO oxidation over Pt3Sn(111) supported SnO2 and (SnO2)(3), representing the initial state of segregation. The results are compared to CO oxidation at an interface between bulk-like SnO2 and Pt3Sn(111). The barrier for CO oxidation via a Mars-van Krevelen mechanism is found to be lower on SnO2 and (SnO2)(3) as compared to the bulk-like model. However, the regeneration of the finite systems is associated with higher barriers for O-2 dissociation which may become the rate limiting step in the low temperature regime where the metal surface can be assumed to be CO covered. |
Kodan, Nisha; Singh, Aadesh P; Vandichel, Matthias; Wickman, Bjorn; Mehta, B R INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 43 (33), pp. 15773-15783, 2018, ISSN: 0360-3199. @article{ISI:000442064100014, title = {Favourable band edge alignment and increased visible light absorption in beta-MoO3/alpha-MoO3 oxide heterojunction for enhanced photoelectrochemical performance}, author = {Nisha Kodan and Aadesh P Singh and Matthias Vandichel and Bjorn Wickman and B R Mehta}, doi = {10.1016/j.ijhydene.2018.06.138}, issn = {0360-3199}, year = {2018}, date = {2018-08-01}, journal = {INTERNATIONAL JOURNAL OF HYDROGEN ENERGY}, volume = {43}, number = {33}, pages = {15773-15783}, abstract = {Optimum band gap values, favourable band edge positions and stability in the electrolyte are critical parameters required for a semiconductor to have efficient photoelectrode properties. The present investigation carried out on the phase pure alpha & beta MoO3 thin film shows that the low bandgap beta-MoO3 possesses a mis-alignment with the water oxidation potential, while a more suitable band alignment is observed for the comparatively large bandgap alpha-MoO3. Both experimental and DFT calculations show that the valence edge of the orthorhombic (alpha-MoO3) phase is located at a higher energy (0.9 eV higher in VB-XPS and 1 eV higher in the DOS plots) than the monoclinic (beta-MoO3) phase, while the conduction edge value is roughly at the same energy level (-2.5 eV) in both polymorphs. Based on the above investigations, an all oxide heterojunction comprising of beta-MoO3/alpha-MoO3 is found to be suitable for improved PEC performance due to favourable energy band diagram and increased visible light absorption in beta-MoO3. Significantly higher cathodic photocurrent is observed for the beta-MoO3/alpha-MoO3 (1.6 mA/cm(2) at applied bias of -0.3V(RHE) under simulated 1 sun irradiation) as compared to the very low anodic response in beta-MoO3 (similar to 1.0 nA/cm(2)) and alpha-MoO3 (32 mu A/cm(2)). (C) 2018 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Optimum band gap values, favourable band edge positions and stability in the electrolyte are critical parameters required for a semiconductor to have efficient photoelectrode properties. The present investigation carried out on the phase pure alpha & beta MoO3 thin film shows that the low bandgap beta-MoO3 possesses a mis-alignment with the water oxidation potential, while a more suitable band alignment is observed for the comparatively large bandgap alpha-MoO3. Both experimental and DFT calculations show that the valence edge of the orthorhombic (alpha-MoO3) phase is located at a higher energy (0.9 eV higher in VB-XPS and 1 eV higher in the DOS plots) than the monoclinic (beta-MoO3) phase, while the conduction edge value is roughly at the same energy level (-2.5 eV) in both polymorphs. Based on the above investigations, an all oxide heterojunction comprising of beta-MoO3/alpha-MoO3 is found to be suitable for improved PEC performance due to favourable energy band diagram and increased visible light absorption in beta-MoO3. Significantly higher cathodic photocurrent is observed for the beta-MoO3/alpha-MoO3 (1.6 mA/cm(2) at applied bias of -0.3V(RHE) under simulated 1 sun irradiation) as compared to the very low anodic response in beta-MoO3 (similar to 1.0 nA/cm(2)) and alpha-MoO3 (32 mu A/cm(2)). (C) 2018 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. |
2017 |
Vandichel, Matthias; Moscu, Alina; Gronbeck, Henrik Catalysis at the Rim: A Mechanism for Low Temperature CO Oxidation over Pt3Sn Journal Article ACS CATALYSIS, 7 (11), pp. 7431-7441, 2017, ISSN: 2155-5435. @article{ISI:000414724700006, title = {Catalysis at the Rim: A Mechanism for Low Temperature CO Oxidation over Pt3Sn}, author = {Matthias Vandichel and Alina Moscu and Henrik Gronbeck}, doi = {10.1021/acscatal.7b02094}, issn = {2155-5435}, year = {2017}, date = {2017-11-01}, journal = {ACS CATALYSIS}, volume = {7}, number = {11}, pages = {7431-7441}, abstract = {Metal alloying is commonly used as a design strategy for catalyst optimization. The mechanistic understanding of this class of systems is, however, obscured by reaction induced segregation phenomena. Herein, the case of CO oxidation over Pt3Sn is investigated using density functional theory calculations combined with ab initio thermodynamics and first-principles based microkinetic modeling. It is found that Pt3Sn segregates under typical operating conditions into SnOx and an Sn deficient metal phase. The segregation is driven both by the stability of the metal oxide and the strong bonding of CO to Pt. The catalytic consequences of a metal supported SnO2 phase are explored by comparing CO oxidation at an SnOx/Pt interface with oxidation over Pt and Pt/Pt3Sn skin models. The reaction is found to proceed with lower barriers at the interface as compared to the metal-only systems and the cocatalytic role of the SnOx rim is manifested by low temperature activity. The present work highlights the effects of reaction-induced metaloxide/metal interfaces and elucidates the role of Sn in PtSn alloys for CO oxidation reactions.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Metal alloying is commonly used as a design strategy for catalyst optimization. The mechanistic understanding of this class of systems is, however, obscured by reaction induced segregation phenomena. Herein, the case of CO oxidation over Pt3Sn is investigated using density functional theory calculations combined with ab initio thermodynamics and first-principles based microkinetic modeling. It is found that Pt3Sn segregates under typical operating conditions into SnOx and an Sn deficient metal phase. The segregation is driven both by the stability of the metal oxide and the strong bonding of CO to Pt. The catalytic consequences of a metal supported SnO2 phase are explored by comparing CO oxidation at an SnOx/Pt interface with oxidation over Pt and Pt/Pt3Sn skin models. The reaction is found to proceed with lower barriers at the interface as compared to the metal-only systems and the cocatalytic role of the SnOx rim is manifested by low temperature activity. The present work highlights the effects of reaction-induced metaloxide/metal interfaces and elucidates the role of Sn in PtSn alloys for CO oxidation reactions. |
Younus, Hussein A; Ahmad, Nazir; Chughtai, Adeel H; Vandichel, Matthias; Busch, Michael; Hecke, Kristof Van; Yusubov, Mekhman; Song, Shaoxian; Verpoort, Francis A Robust Molecular Catalyst Generated In Situ for Photoand Electrochemical Water Oxidation Journal Article CHEMSUSCHEM, 10 (5), pp. 862-875, 2017, ISSN: 1864-5631. @article{ISI:000398182300008, title = {A Robust Molecular Catalyst Generated In Situ for Photoand Electrochemical Water Oxidation}, author = {Hussein A Younus and Nazir Ahmad and Adeel H Chughtai and Matthias Vandichel and Michael Busch and Kristof Van Hecke and Mekhman Yusubov and Shaoxian Song and Francis Verpoort}, doi = {10.1002/cssc.201601477}, issn = {1864-5631}, year = {2017}, date = {2017-03-01}, journal = {CHEMSUSCHEM}, volume = {10}, number = {5}, pages = {862-875}, abstract = {Water splitting is the key step towards artificial photosystems for solar energy conversion and storage in the form of chemical bonding. The oxidation of water is the bottle-neck of this process that hampers its practical utility; hence, efficient, robust, and easy to make catalytic systems based on cheap and earth-abundant materials are of exceptional importance. Herein, an in situ generated cobalt catalyst, [Co-II(TCA)(2)(H2O)(2)] (TCA=1-mesityl-1,2,3-1H-triazole-4-carboxylate), that efficiently conducts photochemical water oxidation under near-neutral conditions is presented. The catalyst showed high stability under photolytic conditions for more than 3 h of photoirradiation. During electrochemical water oxidation, the catalytic system assembled a catalyst film, which proved not to be cobalt oxide/hydroxide as normally expected, but instead, and for the first time, generated a molecular cobalt complex that incorporated the organic ligand bound to cobalt ions. The catalyst film exhibited a low overpotential for electrocatalytic water oxidation (360 mV) and high oxygen evolution peak current densities of 9 and 2.7 mA cm(-2) on glassy carbon and indium-doped tin oxide electrodes, respectively, at only 1.49 and 1.39 V ( versus a normal hydrogen electrode), respectively, under neutral conditions. This finding, exemplified on the in situ generated cobalt complex, might be applicable to other molecular systems and suggests that the formation of a catalytic film in electrochemical water oxidation experiments is not always an indication of catalyst decomposition and the formation of nanoparticles.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Water splitting is the key step towards artificial photosystems for solar energy conversion and storage in the form of chemical bonding. The oxidation of water is the bottle-neck of this process that hampers its practical utility; hence, efficient, robust, and easy to make catalytic systems based on cheap and earth-abundant materials are of exceptional importance. Herein, an in situ generated cobalt catalyst, [Co-II(TCA)(2)(H2O)(2)] (TCA=1-mesityl-1,2,3-1H-triazole-4-carboxylate), that efficiently conducts photochemical water oxidation under near-neutral conditions is presented. The catalyst showed high stability under photolytic conditions for more than 3 h of photoirradiation. During electrochemical water oxidation, the catalytic system assembled a catalyst film, which proved not to be cobalt oxide/hydroxide as normally expected, but instead, and for the first time, generated a molecular cobalt complex that incorporated the organic ligand bound to cobalt ions. The catalyst film exhibited a low overpotential for electrocatalytic water oxidation (360 mV) and high oxygen evolution peak current densities of 9 and 2.7 mA cm(-2) on glassy carbon and indium-doped tin oxide electrodes, respectively, at only 1.49 and 1.39 V ( versus a normal hydrogen electrode), respectively, under neutral conditions. This finding, exemplified on the in situ generated cobalt complex, might be applicable to other molecular systems and suggests that the formation of a catalytic film in electrochemical water oxidation experiments is not always an indication of catalyst decomposition and the formation of nanoparticles. |
Velazquez, Heriberto Diaz; Wu, Zhao-Xuan; Vandichel, Matthias; Verpoort, Francis Inserting CO2 into Terminal Alkynes via Bis-(NHC)-Metal Complexes Journal Article CATALYSIS LETTERS, 147 (2), pp. 463-471, 2017, ISSN: 1011-372X. @article{ISI:000394359600017, title = {Inserting CO2 into Terminal Alkynes via Bis-(NHC)-Metal Complexes}, author = {Heriberto Diaz Velazquez and Zhao-Xuan Wu and Matthias Vandichel and Francis Verpoort}, doi = {10.1007/s10562-016-1920-5}, issn = {1011-372X}, year = {2017}, date = {2017-02-01}, journal = {CATALYSIS LETTERS}, volume = {147}, number = {2}, pages = {463-471}, abstract = {The direct interaction between CO2 and terminal alkynes in the presence of bis-(NHC)-metal catalysts at ambient conditions was studied. Two Cu and Ag-based bis-N-heterocyclic carbene Transition Metal catalysts were synthesized. The (NHC)(2)-Ag complex showed a better catalytic performance towards the carboxylation of terminal alkynes in comparison with the copper analogue even for the conversion of acetylene gas. The optimized conditions for the carboxylation are: the use of Cs2CO3 as additive, one atmosphere CO2 and room temperature using 1% mol catalyst. Mechanistic insight into the reaction mechanism is obtained by means of state-of-the-art first principles calculations. [GRAPHICS] .}, keywords = {}, pubstate = {published}, tppubtype = {article} } The direct interaction between CO2 and terminal alkynes in the presence of bis-(NHC)-metal catalysts at ambient conditions was studied. Two Cu and Ag-based bis-N-heterocyclic carbene Transition Metal catalysts were synthesized. The (NHC)(2)-Ag complex showed a better catalytic performance towards the carboxylation of terminal alkynes in comparison with the copper analogue even for the conversion of acetylene gas. The optimized conditions for the carboxylation are: the use of Cs2CO3 as additive, one atmosphere CO2 and room temperature using 1% mol catalyst. Mechanistic insight into the reaction mechanism is obtained by means of state-of-the-art first principles calculations. [GRAPHICS] . |
2016 |
Filippousi, Maria; Turner, Stuart; Leus, Karen; Siafaka, Panoraia I; Tseligka, Eirini D; Vandichel, Matthias; Nanaki, Stavroula G; Vizirianakis, Ioannis S; Bikiaris, Dimitrios N; der Voort, Pascal Van; Tendeloo, Gustaaf Van Biocompatible Zr-based nanoscale MOFs coated with modified poly (epsilon-caprolactone) as anticancer drug carriers Journal Article INTERNATIONAL JOURNAL OF PHARMACEUTICS, 509 (1-2), pp. 208-218, 2016, ISSN: 0378-5173. @article{ISI:000378949800022, title = {Biocompatible Zr-based nanoscale MOFs coated with modified poly (epsilon-caprolactone) as anticancer drug carriers}, author = {Maria Filippousi and Stuart Turner and Karen Leus and Panoraia I Siafaka and Eirini D Tseligka and Matthias Vandichel and Stavroula G Nanaki and Ioannis S Vizirianakis and Dimitrios N Bikiaris and Pascal Van der Voort and Gustaaf Van Tendeloo}, doi = {10.1016/j.ijpharm.2016.05.048}, issn = {0378-5173}, year = {2016}, date = {2016-07-01}, journal = {INTERNATIONAL JOURNAL OF PHARMACEUTICS}, volume = {509}, number = {1-2}, pages = {208-218}, abstract = {Nanoscale Zr-based metal organic frameworks (MOFs) UiO-66 and UiO-67 were studied as potential anticancer drug delivery vehicles. Two model drugs were used, hydrophobic paclitaxel and hydrophilic cisplatin, and were adsorbed onto/into the nano MOFs (NMOFs). The drug loaded MOFs were further encapsulated inside a modified poly(epsilon-caprolactone) with D-alpha-tocopheryl polyethylene glycol succinate polymeric matrix, in the form of microparticles, in order to prepare sustained release formulations and to reduce the drug toxicity. The drugs physical state and release rate was studied at 37 degrees C using Simulated Body Fluid. It was found that the drug release depends on the interaction between the MOFs and the drugs while the controlled release rates can be attributed to the microencapsulated formulations. The in vitro antitumor activity was assessed using HSC-3 (human oral squamous carcinoma; head and neck) and U-87 MG (human glioblastoma grade IV; astrocytoma) cancer cells. Cytotoxicity studies for both cell lines showed that the polymer coated, drug loaded MOFs exhibited better anticancer activity compared to free paclitaxel and cisplatin solutions at different concentrations. (C) 2016 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Nanoscale Zr-based metal organic frameworks (MOFs) UiO-66 and UiO-67 were studied as potential anticancer drug delivery vehicles. Two model drugs were used, hydrophobic paclitaxel and hydrophilic cisplatin, and were adsorbed onto/into the nano MOFs (NMOFs). The drug loaded MOFs were further encapsulated inside a modified poly(epsilon-caprolactone) with D-alpha-tocopheryl polyethylene glycol succinate polymeric matrix, in the form of microparticles, in order to prepare sustained release formulations and to reduce the drug toxicity. The drugs physical state and release rate was studied at 37 degrees C using Simulated Body Fluid. It was found that the drug release depends on the interaction between the MOFs and the drugs while the controlled release rates can be attributed to the microencapsulated formulations. The in vitro antitumor activity was assessed using HSC-3 (human oral squamous carcinoma; head and neck) and U-87 MG (human glioblastoma grade IV; astrocytoma) cancer cells. Cytotoxicity studies for both cell lines showed that the polymer coated, drug loaded MOFs exhibited better anticancer activity compared to free paclitaxel and cisplatin solutions at different concentrations. (C) 2016 Elsevier B.V. All rights reserved. |
Vandichel, M; Hajek, J; Ghysels, A; Vos, De A; Waroquier, M; Speybroeck, Van V Water coordination and dehydration processes in defective UiO-66 type metal organic frameworks Journal Article CRYSTENGCOMM, 18 (37), pp. 7056-7069, 2016, ISSN: 1466-8033. @article{ISI:000384465500012, title = {Water coordination and dehydration processes in defective UiO-66 type metal organic frameworks}, author = {M Vandichel and J Hajek and A Ghysels and A De Vos and M Waroquier and V Van Speybroeck}, doi = {10.1039/c6ce01027j}, issn = {1466-8033}, year = {2016}, date = {2016-01-01}, journal = {CRYSTENGCOMM}, volume = {18}, number = {37}, pages = {7056-7069}, abstract = {The UiO-66 metal organic framework is one of the most thermally and chemically stable hybrid materials reported to date. However, it is also accepted that the material contains structurally embedded defects, which may be engineered to enhance properties towards specific applications such as catalysis, sensing, etc. The synthesis conditions determine to a large extent the level of perfection of the material and additionally the catalytic activity may be enhanced by post-synthesis activation at high temperature under vacuum, in which defect coordinating species (H2O, HCl, monocarboxylic modulators, etc.) evaporate. The molecular level characterization of defects is extremely challenging from both theoretical and experimental points of view. Such experimental endeavor was recently proposed via experimental SXRD measurements, also unraveling the coordination of water on the Zr-O-Zr defect sites [Angew. Chem., Int. Ed., 2015, 54, 11162-11167]. The present work provides a theoretical understanding of defect structures in UiO-66(Zr) by means of periodic density functional theory calculations and ab initio molecular dynamics simulations. A range of defect structures are generated with different numbers of missing linkers. For each of the defects, the free energetic and mechanical stability is discussed and the coordination of water and charge balancing hydroxide ions is studied. For catalysis applications, the material is mostly pretreated to remove water by dehydration reactions. For each of the proposed defect structures, mechanistic pathways for dehydration reactions of the Zr-bricks are determined employing nudged elastic band (NEB) calculations. During the dehydroxylation trajectory, loose hydroxyl groups and terephthalate decoordinations are observed. Furthermore, dehydration reactions are lower activated if terephthalate linkers are missing in the immediate environment of the inorganic brick. The creation of defects and the dehydration processes have a large impact on the mechanical properties of the material, which is evidenced by lower bulk moduli and elastic constants for structures with more defects.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The UiO-66 metal organic framework is one of the most thermally and chemically stable hybrid materials reported to date. However, it is also accepted that the material contains structurally embedded defects, which may be engineered to enhance properties towards specific applications such as catalysis, sensing, etc. The synthesis conditions determine to a large extent the level of perfection of the material and additionally the catalytic activity may be enhanced by post-synthesis activation at high temperature under vacuum, in which defect coordinating species (H2O, HCl, monocarboxylic modulators, etc.) evaporate. The molecular level characterization of defects is extremely challenging from both theoretical and experimental points of view. Such experimental endeavor was recently proposed via experimental SXRD measurements, also unraveling the coordination of water on the Zr-O-Zr defect sites [Angew. Chem., Int. Ed., 2015, 54, 11162-11167]. The present work provides a theoretical understanding of defect structures in UiO-66(Zr) by means of periodic density functional theory calculations and ab initio molecular dynamics simulations. A range of defect structures are generated with different numbers of missing linkers. For each of the defects, the free energetic and mechanical stability is discussed and the coordination of water and charge balancing hydroxide ions is studied. For catalysis applications, the material is mostly pretreated to remove water by dehydration reactions. For each of the proposed defect structures, mechanistic pathways for dehydration reactions of the Zr-bricks are determined employing nudged elastic band (NEB) calculations. During the dehydroxylation trajectory, loose hydroxyl groups and terephthalate decoordinations are observed. Furthermore, dehydration reactions are lower activated if terephthalate linkers are missing in the immediate environment of the inorganic brick. The creation of defects and the dehydration processes have a large impact on the mechanical properties of the material, which is evidenced by lower bulk moduli and elastic constants for structures with more defects. |
Canivet, J; Vandichel, M; Farrusseng, D Origin of highly active metal-organic framework catalysts: defects? Defects! Journal Article DALTON TRANSACTIONS, 45 (10), pp. 4090-4099, 2016, ISSN: 1477-9226. @article{ISI:000371710500004, title = {Origin of highly active metal-organic framework catalysts: defects? Defects!}, author = {J Canivet and M Vandichel and D Farrusseng}, doi = {10.1039/c5dt03522h}, issn = {1477-9226}, year = {2016}, date = {2016-01-01}, journal = {DALTON TRANSACTIONS}, volume = {45}, number = {10}, pages = {4090-4099}, abstract = {This article provides a comprehensive review of the nature of catalytic sites in MOFs. In the last decade, a number of striking studies have reported outstanding catalytic activities of MOFs. In all cases, the authors were intrigued as it was unexpected from the ideal structure. We demonstrate here that (surface) defects are at the origin of the catalytic activities for the reported examples. The vacancy of ligands or linkers systematically generates (surface) terminations which can possibly show Lewis and/or Bronsted acido-basic features. The engineering of catalytic sites at the nodes by the creation of defects (on purpose) appears today as a rational approach for the design of active MOFs. Similarly to zeolite post-treatments, post-modifications of MOFs by linker or metal cation exchange appear to be methods of choice. Despite the mild acidity of defective MOFs, we can account for very active MOFs in a number of catalytic applications which show higher performances than zeolites or benchmark catalysts.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This article provides a comprehensive review of the nature of catalytic sites in MOFs. In the last decade, a number of striking studies have reported outstanding catalytic activities of MOFs. In all cases, the authors were intrigued as it was unexpected from the ideal structure. We demonstrate here that (surface) defects are at the origin of the catalytic activities for the reported examples. The vacancy of ligands or linkers systematically generates (surface) terminations which can possibly show Lewis and/or Bronsted acido-basic features. The engineering of catalytic sites at the nodes by the creation of defects (on purpose) appears today as a rational approach for the design of active MOFs. Similarly to zeolite post-treatments, post-modifications of MOFs by linker or metal cation exchange appear to be methods of choice. Despite the mild acidity of defective MOFs, we can account for very active MOFs in a number of catalytic applications which show higher performances than zeolites or benchmark catalysts. |
2015 |
Hajek, Julianna; Vandichel, Matthias; de Voorde, Ben Van; Bueken, Bart; Vos, Dirk De; Waroquier, Michel; Speybroeck, Veronique Van Mechanistic studies of aldol condensations in UiO-66 and UiO-66-NH2 metal organic frameworks Journal Article JOURNAL OF CATALYSIS, 331 , pp. 1-12, 2015, ISSN: 0021-9517. @article{ISI:000364250800001, title = {Mechanistic studies of aldol condensations in UiO-66 and UiO-66-NH2 metal organic frameworks}, author = {Julianna Hajek and Matthias Vandichel and Ben Van de Voorde and Bart Bueken and Dirk De Vos and Michel Waroquier and Veronique Van Speybroeck}, doi = {10.1016/j.jcat.2015.08.015}, issn = {0021-9517}, year = {2015}, date = {2015-11-01}, journal = {JOURNAL OF CATALYSIS}, volume = {331}, pages = {1-12}, abstract = {A full mechanistic investigation is proposed for the industrially important cross-aldol condensation reaction of heptanal with benzaldehyde on the UiO-66 and the amino-functionalized UiO-66-NH2 metal-organic frameworks to form jasminaldehyde. Several experimental studies indicate that the activity for the aldol condensation reaction can be increased by proper functionalization of the material, e.g. by introducing an additional basic amino site and thus creating a bifunctional acid-base catalyst for the aldol condensation. The precise molecular level origin for this behavior is to date unclear. Herein state-of-the-art Density-Functional Theory (DFT) calculations have been performed to unravel the mechanism of the cross- and self-aldol condensations of benzaldehyde and propanal. To this end free energy calculations have been performed on both extended cluster and periodic models. It is found that the mechanism on both catalysts is essentially the same, although a slightly stronger adsorption of the reactants and slightly lower barriers were found on the amino functionalized material, pointing toward higher initial activities. New experiments were performed to confirm these observations. It is indeed found that the initial activity toward cross-aldol condensation on the amino functionalized material is higher, although after about 40 min of reaction both materials become equally active. Our results furthermore point out that the basic amino groups may promote side reactions such as imine formation, which is induced by water. The study as presented can assist to engineer materials at the molecular level toward the desired products. (C) 2015 Elsevier Inc. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A full mechanistic investigation is proposed for the industrially important cross-aldol condensation reaction of heptanal with benzaldehyde on the UiO-66 and the amino-functionalized UiO-66-NH2 metal-organic frameworks to form jasminaldehyde. Several experimental studies indicate that the activity for the aldol condensation reaction can be increased by proper functionalization of the material, e.g. by introducing an additional basic amino site and thus creating a bifunctional acid-base catalyst for the aldol condensation. The precise molecular level origin for this behavior is to date unclear. Herein state-of-the-art Density-Functional Theory (DFT) calculations have been performed to unravel the mechanism of the cross- and self-aldol condensations of benzaldehyde and propanal. To this end free energy calculations have been performed on both extended cluster and periodic models. It is found that the mechanism on both catalysts is essentially the same, although a slightly stronger adsorption of the reactants and slightly lower barriers were found on the amino functionalized material, pointing toward higher initial activities. New experiments were performed to confirm these observations. It is indeed found that the initial activity toward cross-aldol condensation on the amino functionalized material is higher, although after about 40 min of reaction both materials become equally active. Our results furthermore point out that the basic amino groups may promote side reactions such as imine formation, which is induced by water. The study as presented can assist to engineer materials at the molecular level toward the desired products. (C) 2015 Elsevier Inc. All rights reserved. |
Vandichel, Matthias; Hajek, Julianna; Vermoortele, Frederik; Waroquier, Michel; Vos, Dirk De E; Speybroeck, Veronique Van Active site engineering in UiO-66 type metal-organic frameworks by intentional creation of defects: a theoretical rationalization Journal Article CRYSTENGCOMM, 17 (2), pp. 395-406, 2015, ISSN: 1466-8033. @article{ISI:000346173200024, title = {Active site engineering in UiO-66 type metal-organic frameworks by intentional creation of defects: a theoretical rationalization}, author = {Matthias Vandichel and Julianna Hajek and Frederik Vermoortele and Michel Waroquier and Dirk E De Vos and Veronique Van Speybroeck}, doi = {10.1039/c4ce01672f}, issn = {1466-8033}, year = {2015}, date = {2015-01-01}, journal = {CRYSTENGCOMM}, volume = {17}, number = {2}, pages = {395-406}, abstract = {The catalytic activity of the Zr-benzenedicarboxylate (Zr-BDC) UiO-66 can be drastically increased if some BDC linkers are missing, as this removes the full coordination of the framework metal ions. As a result, metal centers become more accessible and thus more active for Lewis acid catalysed reactions. Addition of modulators (MDL) to the synthesis mixture can create more linker deficiencies (Vermoortele et al., J. Am. Chem. Soc., 2013, 135, 11465) and leads to a significant increase in the catalytic activity due to the creation of a larger number of open sites. In this paper, we rationalize the function of the modulators under real synthesis conditions by the construction of free energy diagrams. The UiO-66 type materials form a very appropriate test case as the effect of addition of modulators hydrochloric acid (HCl) and trifluoroacetate (TFA) has been intensively investigated experimentally for the synthesis process and post-synthetic thermal activation. Under synthesis conditions, direct removal of BDC linkers requires a high free energy, but replacement of such linker by one or more TFA species might occur especially at high TFA : BDC ratios in the reaction mixture. Post-synthesis activation procedures at higher temperatures lead to substantial removal of the species coordinated to the Zr bricks, creating open metal sites. A mechanistic pathway is presented for the dehydroxylation process of the hexanuclear Zr cluster. For the citronellal cyclization, we show that the presence of some residual TFA in the structure may lead to faster reactions in complete agreement with the experiment. Hirshfeld-e partial charges for the Zr ions have been computed to investigate their sensitivity to substituent effects; a strong correlation with the experimental Hammett parameters and with the rates of the citronellal cyclization is found. The theoretical rationalization may serve as a basis for detailed active site engineering studies.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The catalytic activity of the Zr-benzenedicarboxylate (Zr-BDC) UiO-66 can be drastically increased if some BDC linkers are missing, as this removes the full coordination of the framework metal ions. As a result, metal centers become more accessible and thus more active for Lewis acid catalysed reactions. Addition of modulators (MDL) to the synthesis mixture can create more linker deficiencies (Vermoortele et al., J. Am. Chem. Soc., 2013, 135, 11465) and leads to a significant increase in the catalytic activity due to the creation of a larger number of open sites. In this paper, we rationalize the function of the modulators under real synthesis conditions by the construction of free energy diagrams. The UiO-66 type materials form a very appropriate test case as the effect of addition of modulators hydrochloric acid (HCl) and trifluoroacetate (TFA) has been intensively investigated experimentally for the synthesis process and post-synthetic thermal activation. Under synthesis conditions, direct removal of BDC linkers requires a high free energy, but replacement of such linker by one or more TFA species might occur especially at high TFA : BDC ratios in the reaction mixture. Post-synthesis activation procedures at higher temperatures lead to substantial removal of the species coordinated to the Zr bricks, creating open metal sites. A mechanistic pathway is presented for the dehydroxylation process of the hexanuclear Zr cluster. For the citronellal cyclization, we show that the presence of some residual TFA in the structure may lead to faster reactions in complete agreement with the experiment. Hirshfeld-e partial charges for the Zr ions have been computed to investigate their sensitivity to substituent effects; a strong correlation with the experimental Hammett parameters and with the rates of the citronellal cyclization is found. The theoretical rationalization may serve as a basis for detailed active site engineering studies. |
Leus, K; Concepcion, P; Vandichel, M; Meledina, M; Grirrane, A; Esquivel, D; Turner, S; Poelman, D; Waroquier, M; Speybroeck, Van V; Tendeloo, Van G; Garcia, H; Voort, Van Der P Au@UiO-66: a base free oxidation catalyst Journal Article RSC ADVANCES, 5 (29), pp. 22334-22342, 2015, ISSN: 2046-2069. @article{ISI:000350643700005, title = {Au@UiO-66: a base free oxidation catalyst}, author = {K Leus and P Concepcion and M Vandichel and M Meledina and A Grirrane and D Esquivel and S Turner and D Poelman and M Waroquier and V Van Speybroeck and G Van Tendeloo and H Garcia and P Van Der Voort}, doi = {10.1039/c4ra16800c}, issn = {2046-2069}, year = {2015}, date = {2015-01-01}, journal = {RSC ADVANCES}, volume = {5}, number = {29}, pages = {22334-22342}, abstract = {We present the in situ synthesis of Au nanoparticles within the Zr based Metal Organic Framework, UiO-66. The resulting Au@UiO-66 materials were characterized by means of N-2 sorption, XRPD, UV-Vis, XRF, XPS and TEM analysis. The Au nanoparticles (NP) are homogeneously distributed along the UiO-66 host matrix when using NaBH4 or H-2 as reducing agents. The Au@UiO-66 materials were evaluated as catalysts in the oxidation of benzyl alcohol and benzyl amine employing O-2 as oxidant. The Au@MOF materials exhibit a very high selectivity towards the ketone (up to 100%). Regenerability and stability tests demonstrate that the Au@UiO-66 catalyst can be recycled with a negligible loss of Au species and no loss of crystallinity. In situ IR measurements of UiO-66 and Au@UiO-66-NaBH4, before and after treatment with alcohol, showed an increase in IR bands that can be assigned to a combination of physisorbed and chemisorbed alcohol species. This was confirmed by velocity power spectra obtained from the molecular dynamics simulations. Active peroxo and oxo species on Au could be visualized with Raman analysis.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We present the in situ synthesis of Au nanoparticles within the Zr based Metal Organic Framework, UiO-66. The resulting Au@UiO-66 materials were characterized by means of N-2 sorption, XRPD, UV-Vis, XRF, XPS and TEM analysis. The Au nanoparticles (NP) are homogeneously distributed along the UiO-66 host matrix when using NaBH4 or H-2 as reducing agents. The Au@UiO-66 materials were evaluated as catalysts in the oxidation of benzyl alcohol and benzyl amine employing O-2 as oxidant. The Au@MOF materials exhibit a very high selectivity towards the ketone (up to 100%). Regenerability and stability tests demonstrate that the Au@UiO-66 catalyst can be recycled with a negligible loss of Au species and no loss of crystallinity. In situ IR measurements of UiO-66 and Au@UiO-66-NaBH4, before and after treatment with alcohol, showed an increase in IR bands that can be assigned to a combination of physisorbed and chemisorbed alcohol species. This was confirmed by velocity power spectra obtained from the molecular dynamics simulations. Active peroxo and oxo species on Au could be visualized with Raman analysis. |
Leus, K; Concepcion, P; Vandichel, M; Meledina, M; Grirrane, A; Esquivel, D; Turner, S; Poelman, D; Waroquier, M; Speybroeck, Van V; Tendeloo, Van G; Garcia, H; der Voort, Van P Au@UiO-66: a base free oxidation catalyst (vol 5, pg 22334, 2015) Journal Article RSC ADVANCES, 5 (34), pp. 26726, 2015, ISSN: 2046-2069. @article{ISI:000351556800034, title = {Au@UiO-66: a base free oxidation catalyst (vol 5, pg 22334, 2015)}, author = {K Leus and P Concepcion and M Vandichel and M Meledina and A Grirrane and D Esquivel and S Turner and D Poelman and M Waroquier and V Van Speybroeck and G Van Tendeloo and H Garcia and P Van der Voort}, doi = {10.1039/c5ra90022k}, issn = {2046-2069}, year = {2015}, date = {2015-01-01}, journal = {RSC ADVANCES}, volume = {5}, number = {34}, pages = {26726}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2014 |
Vandichel, Matthias; Biswas, Shyam; Leus, Karen; Paier, Joachim; Sauer, Joachim; Verstraelen, Toon; der Voort, Pascal Van; Waroquier, Michel; Speybroeck, Veronique Van CHEMPLUSCHEM, 79 (8), pp. 1183-1197, 2014, ISSN: 2192-6506. @article{ISI:000340508000016, title = {Catalytic Performance of Vanadium MIL-47 and Linker-Substituted Variants in the Oxidation of Cyclohexene: A Combined Theoretical and Experimental Approach}, author = {Matthias Vandichel and Shyam Biswas and Karen Leus and Joachim Paier and Joachim Sauer and Toon Verstraelen and Pascal Van der Voort and Michel Waroquier and Veronique Van Speybroeck}, doi = {10.1002/cplu.201402007}, issn = {2192-6506}, year = {2014}, date = {2014-08-01}, journal = {CHEMPLUSCHEM}, volume = {79}, number = {8}, pages = {1183-1197}, abstract = {The epoxidation of cyclohexene has been investigated on a metal-organic framework MIL-47 containing saturated V+IV sites linked with functionalized terephthalate linkers (MIL-47-X}, keywords = {}, pubstate = {published}, tppubtype = {article} } The epoxidation of cyclohexene has been investigated on a metal-organic framework MIL-47 containing saturated V+IV sites linked with functionalized terephthalate linkers (MIL-47-X |
Valvekens, Pieterjan; Vandichel, Matthias; Waroquier, Michel; Speybroeck, Veronique Van; Vos, Dirk De Metal-dioxidoterephthalate MOFs of the MOF-74 type: Microporous basic catalysts with well-defined active sites Journal Article JOURNAL OF CATALYSIS, 317 , pp. 1-10, 2014, ISSN: 0021-9517. @article{ISI:000341473000001, title = {Metal-dioxidoterephthalate MOFs of the MOF-74 type: Microporous basic catalysts with well-defined active sites}, author = {Pieterjan Valvekens and Matthias Vandichel and Michel Waroquier and Veronique Van Speybroeck and Dirk De Vos}, doi = {10.1016/j.jcat.2014.06.006}, issn = {0021-9517}, year = {2014}, date = {2014-08-01}, journal = {JOURNAL OF CATALYSIS}, volume = {317}, pages = {1-10}, abstract = {The hybrid frameworks M(2)dobdc (dobdc(4-) = 2,5-dioxidoterephthalate, M2+ = Mg2+, Co2+, Ni2+, Cu2+ and Zn2+), commonly known as CPO-27 or MOF-74, are shown to be active catalysts in base-catalyzed reactions such as Knoevenagel condensations or Michael additions. Rather than utilizing N-functionalized linkers as a source of basicity, the intrinsic basicity of these materials arises from the presence of the phenolate oxygen atoms coordinated to the metal ions. The overall activity is due to a complex interplay of the basic properties of these structural phenolates and the reactant binding characteristics of the coordinatively unsaturated sites. The nature of the active site and the order of activity between the different M(2)dobdc materials were rationalized via computational efforts; the most active material, both in theory and in experiment, is the Ni-containing variant. The basicity of Ni(2)dobdc was experimentally proven by chemisorption of pyrrole and observation by IR spectroscopy. (C) 2014 Elsevier Inc. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The hybrid frameworks M(2)dobdc (dobdc(4-) = 2,5-dioxidoterephthalate, M2+ = Mg2+, Co2+, Ni2+, Cu2+ and Zn2+), commonly known as CPO-27 or MOF-74, are shown to be active catalysts in base-catalyzed reactions such as Knoevenagel condensations or Michael additions. Rather than utilizing N-functionalized linkers as a source of basicity, the intrinsic basicity of these materials arises from the presence of the phenolate oxygen atoms coordinated to the metal ions. The overall activity is due to a complex interplay of the basic properties of these structural phenolates and the reactant binding characteristics of the coordinatively unsaturated sites. The nature of the active site and the order of activity between the different M(2)dobdc materials were rationalized via computational efforts; the most active material, both in theory and in experiment, is the Ni-containing variant. The basicity of Ni(2)dobdc was experimentally proven by chemisorption of pyrrole and observation by IR spectroscopy. (C) 2014 Elsevier Inc. All rights reserved. |
Valvekens, P; Jonckheere, D; Baerdemaeker, De T; Kubarev, A V; Vandichel, M; Hemelsoet, K; Waroquier, M; Speybroeck, Van V; Smolders, E; Depla, D; Roeffaers, M B J; Vos, De D CHEMICAL SCIENCE, 5 (11), pp. 4517-4524, 2014, ISSN: 2041-6520. @article{ISI:000343004300050, title = {Base catalytic activity of alkaline earth MOFs: a (micro)spectroscopic study of active site formation by the controlled transformation of structural anions}, author = {P Valvekens and D Jonckheere and T De Baerdemaeker and A V Kubarev and M Vandichel and K Hemelsoet and M Waroquier and V Van Speybroeck and E Smolders and D Depla and M B J Roeffaers and D De Vos}, doi = {10.1039/c4sc01731e}, issn = {2041-6520}, year = {2014}, date = {2014-01-01}, journal = {CHEMICAL SCIENCE}, volume = {5}, number = {11}, pages = {4517-4524}, abstract = {A new method has been developed for generating highly dispersed base sites on metal-organic framework (MOF) lattices. The base catalytic activity of two alkaline earth MOFs, M-2(BTC)(NO3)(DMF) (M = Ba or Sr}, keywords = {}, pubstate = {published}, tppubtype = {article} } A new method has been developed for generating highly dispersed base sites on metal-organic framework (MOF) lattices. The base catalytic activity of two alkaline earth MOFs, M-2(BTC)(NO3)(DMF) (M = Ba or Sr |
Speybroeck, Veronique Van; Wispelaere, Kristof De; der Mynsbrugge, Jeroen Van; Vandichel, Matthias; Hemelsoet, Karen; Waroquier, Michel First principle chemical kinetics in zeolites: the methanol-to-olefin process as a case study Journal Article CHEMICAL SOCIETY REVIEWS, 43 (21), pp. 7326-7357, 2014, ISSN: 0306-0012. @article{ISI:000342908200006, title = {First principle chemical kinetics in zeolites: the methanol-to-olefin process as a case study}, author = {Veronique Van Speybroeck and Kristof De Wispelaere and Jeroen Van der Mynsbrugge and Matthias Vandichel and Karen Hemelsoet and Michel Waroquier}, doi = {10.1039/c4cs00146j}, issn = {0306-0012}, year = {2014}, date = {2014-01-01}, journal = {CHEMICAL SOCIETY REVIEWS}, volume = {43}, number = {21}, pages = {7326-7357}, abstract = {To optimally design next generation catalysts a thorough understanding of the chemical phenomena at the molecular scale is a prerequisite. Apart from qualitative knowledge on the reaction mechanism, it is also essential to be able to predict accurate rate constants. Molecular modeling has become a ubiquitous tool within the field of heterogeneous catalysis. Herein, we review current computational procedures to determine chemical kinetics from first principles, thus by using no experimental input and by modeling the catalyst and reacting species at the molecular level. Therefore, we use the methanol-to- olefin (MTO) process as a case study to illustrate the various theoretical concepts. This process is a showcase example where rational design of the catalyst was for a long time performed on the basis of trial and error, due to insufficient knowledge of the mechanism. For theoreticians the MTO process is particularly challenging as the catalyst has an inherent supramolecular nature, for which not only the Bronsted acidic site is important but also organic species, trapped in the zeolite pores, must be essentially present during active catalyst operation. All these aspects give rise to specific challenges for theoretical modeling. It is shown that present computational techniques have matured to a level where accurate enthalpy barriers and rate constants can be predicted for reactions occurring at a single active site. The comparison with experimental data such as apparent kinetic data for well-defined elementary reactions has become feasible as current computational techniques also allow predicting adsorption enthalpies with reasonable accuracy. Real catalysts are truly heterogeneous in a space-and time-like manner. Future theory developments should focus on extending our view towards phenomena occurring at longer length and time scales and integrating information from various scales towards a unified understanding of the catalyst. Within this respect molecular dynamics methods complemented with additional techniques to simulate rare events are now gradually making their entrance within zeolite catalysis. Recent applications have already given a flavor of the benefit of such techniques to simulate chemical reactions in complex molecular environments.}, keywords = {}, pubstate = {published}, tppubtype = {article} } To optimally design next generation catalysts a thorough understanding of the chemical phenomena at the molecular scale is a prerequisite. Apart from qualitative knowledge on the reaction mechanism, it is also essential to be able to predict accurate rate constants. Molecular modeling has become a ubiquitous tool within the field of heterogeneous catalysis. Herein, we review current computational procedures to determine chemical kinetics from first principles, thus by using no experimental input and by modeling the catalyst and reacting species at the molecular level. Therefore, we use the methanol-to- olefin (MTO) process as a case study to illustrate the various theoretical concepts. This process is a showcase example where rational design of the catalyst was for a long time performed on the basis of trial and error, due to insufficient knowledge of the mechanism. For theoreticians the MTO process is particularly challenging as the catalyst has an inherent supramolecular nature, for which not only the Bronsted acidic site is important but also organic species, trapped in the zeolite pores, must be essentially present during active catalyst operation. All these aspects give rise to specific challenges for theoretical modeling. It is shown that present computational techniques have matured to a level where accurate enthalpy barriers and rate constants can be predicted for reactions occurring at a single active site. The comparison with experimental data such as apparent kinetic data for well-defined elementary reactions has become feasible as current computational techniques also allow predicting adsorption enthalpies with reasonable accuracy. Real catalysts are truly heterogeneous in a space-and time-like manner. Future theory developments should focus on extending our view towards phenomena occurring at longer length and time scales and integrating information from various scales towards a unified understanding of the catalyst. Within this respect molecular dynamics methods complemented with additional techniques to simulate rare events are now gradually making their entrance within zeolite catalysis. Recent applications have already given a flavor of the benefit of such techniques to simulate chemical reactions in complex molecular environments. |
der Voort, Pascal Van; Leus, Karen; Liu, Ying-Ya; Vandichel, Matthias; Speybroeck, Veronique Van; Waroquier, Michel; Biswas, Shyam Vanadium metal-organic frameworks: structures and applications Journal Article NEW JOURNAL OF CHEMISTRY, 38 (5), pp. 1853-1867, 2014, ISSN: 1144-0546. @article{ISI:000334832200006, title = {Vanadium metal-organic frameworks: structures and applications}, author = {Pascal Van der Voort and Karen Leus and Ying-Ya Liu and Matthias Vandichel and Veronique Van Speybroeck and Michel Waroquier and Shyam Biswas}, doi = {10.1039/c3nj01130e}, issn = {1144-0546}, year = {2014}, date = {2014-01-01}, journal = {NEW JOURNAL OF CHEMISTRY}, volume = {38}, number = {5}, pages = {1853-1867}, abstract = {This perspective review paper describes the V-containing metal-organic frameworks that have been developed since the first systematic reports on MOFs almost 15 years ago. These hybrid crystalline materials, containing V(III) or V(IV) as metal nodes, show interesting behavior in oxidation catalysis and gas sorption. A significant amount of papers has appeared on the use of these structures in gas (hydrocarbon, CO2) separation. Promising future research and development of V-MOFs is suggested.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This perspective review paper describes the V-containing metal-organic frameworks that have been developed since the first systematic reports on MOFs almost 15 years ago. These hybrid crystalline materials, containing V(III) or V(IV) as metal nodes, show interesting behavior in oxidation catalysis and gas sorption. A significant amount of papers has appeared on the use of these structures in gas (hydrocarbon, CO2) separation. Promising future research and development of V-MOFs is suggested. |
Velazquez, Heriberto Diaz; Garcia, Yara Ruiz; Vandichel, Matthias; Madder, Annemieke; Verpoort, Francis Water-soluble NHC-Cu catalysts: applications in click chemistry, bioconjugation and mechanistic analysis Journal Article ORGANIC & BIOMOLECULAR CHEMISTRY, 12 (46), pp. 9350-9356, 2014, ISSN: 1477-0520. @article{ISI:000344989700010, title = {Water-soluble NHC-Cu catalysts: applications in click chemistry, bioconjugation and mechanistic analysis}, author = {Heriberto Diaz Velazquez and Yara Ruiz Garcia and Matthias Vandichel and Annemieke Madder and Francis Verpoort}, doi = {10.1039/c4ob01350f}, issn = {1477-0520}, year = {2014}, date = {2014-01-01}, journal = {ORGANIC & BIOMOLECULAR CHEMISTRY}, volume = {12}, number = {46}, pages = {9350-9356}, abstract = {Copper(I)-catalyzed 1,3-dipolar cycloaddition of azides and terminal alkynes (CuAAC), better known as ``click'' reaction, has triggered the use of 1,2,3-triazoles in bioconjugation, drug discovery, materials science and combinatorial chemistry. Here we report a new series of water-soluble catalysts based on N-heterocyclic carbene (NHC)-Cu complexes which are additionally functionalized with a sulfonate group. The complexes show superior activity towards CuAAC reactions and display a high versatility, enabling the production of triazoles with different substitution patterns. Additionally, successful application of these complexes in bioconjugation using unprotected peptides acting as DNA binding domains was achieved for the first time. Mechanistic insight into the reaction mechanism is obtained by means of state-of-the-art first principles calculations.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Copper(I)-catalyzed 1,3-dipolar cycloaddition of azides and terminal alkynes (CuAAC), better known as ``click'' reaction, has triggered the use of 1,2,3-triazoles in bioconjugation, drug discovery, materials science and combinatorial chemistry. Here we report a new series of water-soluble catalysts based on N-heterocyclic carbene (NHC)-Cu complexes which are additionally functionalized with a sulfonate group. The complexes show superior activity towards CuAAC reactions and display a high versatility, enabling the production of triazoles with different substitution patterns. Additionally, successful application of these complexes in bioconjugation using unprotected peptides acting as DNA binding domains was achieved for the first time. Mechanistic insight into the reaction mechanism is obtained by means of state-of-the-art first principles calculations. |
2013 |
Biswas, Shyam; Vanpoucke, Danny E P; Verstraelen, Toon; Vandichel, Matthias; Couck, Sarah; Leus, Karen; Liu, Ying-Ya; Waroquier, Michel; Speybroeck, Veronique Van; Denayer, Joeri F M; der Voort, Pascal Van JOURNAL OF PHYSICAL CHEMISTRY C, 117 (44), pp. 22784-22796, 2013, ISSN: 1932-7447. @article{ISI:000326845400037, title = {New Functionalized Metal-Organic Frameworks MIL-47-X (X = -Cl, -Br, -CH3, -CF3, -OH, -OCH3): Synthesis, Characterization, and CO2 Adsorption Properties}, author = {Shyam Biswas and Danny E P Vanpoucke and Toon Verstraelen and Matthias Vandichel and Sarah Couck and Karen Leus and Ying-Ya Liu and Michel Waroquier and Veronique Van Speybroeck and Joeri F M Denayer and Pascal Van der Voort}, doi = {10.1021/jp406835n}, issn = {1932-7447}, year = {2013}, date = {2013-11-01}, journal = {JOURNAL OF PHYSICAL CHEMISTRY C}, volume = {117}, number = {44}, pages = {22784-22796}, abstract = {Six new functionalized vanadium hydroxo terephthalates [V-III(OH)(BDC-X)]center dot n(guests) (MIL-47(V-III)-X-AS) (BDC = 1,4-benzenedicarboxylate; X = -Cl, -Br, -CH3, -CF3, -OH, -OCH3; AS = as-synthesized) along with the parent MIL-47 were synthesized under rapid microwave-assisted hydrothermal conditions (170 degrees C, 30 min, 150 W). The unreacted H2BDC-X and/or occluded solvent molecules can be removed by thermal activation under vacuum, leading to the empty-pore forms of the title compounds (MIL-47(V-IV)-X). Except pristine MIL-47 (+III oxidation state), the vanadium atoms in all the evacuated functionalized solids stayed in the +IV oxidation state. The phase purity of the compounds was ascertained by X-ray powder diffraction (XRPD), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, Raman, thermogravimetric (TG), and elemental analysis. The structural similarity of the filled and empty-pore forms of the functionalized compounds with the respective forms of parent MIL-47 was verified by cell parameter determination from XRPD data. TGA and temperature-dependent XRPD (TDXRPD) experiments in an air atmosphere indicate high thermal stability in the 330-385 degrees C range. All the thermally activated compounds exhibit significant microporosity (S-BET in the 305-897 m(2) g(-1) range), as verified by the N-2 and CO2 sorption analysis. Among the six functionalized compounds, MIL-47(V-IV)-OCH3 shows the highest CO2 uptake, demonstrating the determining role of functional groups on the CO2 sorption behavior. For this compound and pristine MIL-47(V-IV), Widom particle insertion simulations were performed based on ab initio calculated crystal structures. The theoretical Henry coefficients show a good agreement with the experimental values, and calculated isosurfaces for the local excess chemical potential indicate the enhanced CO2 affinity is due to two effects: (i) the interaction between the methoxy group and CO2 and (ii) the collapse of the MIL-47(V-IV)-OCH3 framework.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Six new functionalized vanadium hydroxo terephthalates [V-III(OH)(BDC-X)]center dot n(guests) (MIL-47(V-III)-X-AS) (BDC = 1,4-benzenedicarboxylate; X = -Cl, -Br, -CH3, -CF3, -OH, -OCH3; AS = as-synthesized) along with the parent MIL-47 were synthesized under rapid microwave-assisted hydrothermal conditions (170 degrees C, 30 min, 150 W). The unreacted H2BDC-X and/or occluded solvent molecules can be removed by thermal activation under vacuum, leading to the empty-pore forms of the title compounds (MIL-47(V-IV)-X). Except pristine MIL-47 (+III oxidation state), the vanadium atoms in all the evacuated functionalized solids stayed in the +IV oxidation state. The phase purity of the compounds was ascertained by X-ray powder diffraction (XRPD), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, Raman, thermogravimetric (TG), and elemental analysis. The structural similarity of the filled and empty-pore forms of the functionalized compounds with the respective forms of parent MIL-47 was verified by cell parameter determination from XRPD data. TGA and temperature-dependent XRPD (TDXRPD) experiments in an air atmosphere indicate high thermal stability in the 330-385 degrees C range. All the thermally activated compounds exhibit significant microporosity (S-BET in the 305-897 m(2) g(-1) range), as verified by the N-2 and CO2 sorption analysis. Among the six functionalized compounds, MIL-47(V-IV)-OCH3 shows the highest CO2 uptake, demonstrating the determining role of functional groups on the CO2 sorption behavior. For this compound and pristine MIL-47(V-IV), Widom particle insertion simulations were performed based on ab initio calculated crystal structures. The theoretical Henry coefficients show a good agreement with the experimental values, and calculated isosurfaces for the local excess chemical potential indicate the enhanced CO2 affinity is due to two effects: (i) the interaction between the methoxy group and CO2 and (ii) the collapse of the MIL-47(V-IV)-OCH3 framework. |
Vandichel, Matthias; Vermoortele, Frederik; Cottenie, Stijn; Vos, Dirk De E; Waroquier, Michel; Speybroeck, Veronique Van Insight in the activity and diastereoselectivity of various Lewis acid catalysts for the citronellal cyclization Journal Article JOURNAL OF CATALYSIS, 305 , pp. 118-129, 2013, ISSN: 0021-9517. @article{ISI:000322501000013, title = {Insight in the activity and diastereoselectivity of various Lewis acid catalysts for the citronellal cyclization}, author = {Matthias Vandichel and Frederik Vermoortele and Stijn Cottenie and Dirk E De Vos and Michel Waroquier and Veronique Van Speybroeck}, doi = {10.1016/j.jcat.2013.04.017}, issn = {0021-9517}, year = {2013}, date = {2013-09-01}, journal = {JOURNAL OF CATALYSIS}, volume = {305}, pages = {118-129}, abstract = {Industrial (-)-menthol production generally relies on the hydrogenation of (-)-isopulegol, which is in turn produced with high selectivity by cyclization of (+)-citronellal. This paper uses a combined theoretical and experimental approach to study the activity and selectivity of three Lewis acid catalysts for this reaction, namely ZnBr2, aluminum tris(2,6-diphenylphenoxide) (ATPH), and the heterogeneous metal-organic framework Cu3BTC2 (BTC = benzene-1,3,5-tricarboxylate). ATPH is a strong Lewis acid homogeneous catalyst with bulky ligands which provides very high selectivities for the desired stereoisomer (>99%). The performance of the catalysts was evaluated as a function of temperature, which revealed that a higher catalyst activity allows working at lower temperatures and improves the selectivity for isopulegol. The selectivity distribution is kinetically driven for ZnBr2 and ATPH. The theoretical selectivity distributions rely on the determination of an extensive set of diastereomeric transition states, for which the differences in free energy have been calculated using a complementary set of ab initio techniques. Given the sensitivity of the selectivity to small Gibbs free-energy differences, the agreement between experimental and theoretical selectivities is satisfactory. On basis of the obtained insights, rational design of new catalysts may be obtained. As proof of concept, the hypothetical Cu-3(BTC-(NO2)(3))(2) Lewis catalyst - in which each phenyl hydrogen of the BTC ligand is replaced by a nitro group - is predicted to be very selective. (C) 2013 Elsevier Inc. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Industrial (-)-menthol production generally relies on the hydrogenation of (-)-isopulegol, which is in turn produced with high selectivity by cyclization of (+)-citronellal. This paper uses a combined theoretical and experimental approach to study the activity and selectivity of three Lewis acid catalysts for this reaction, namely ZnBr2, aluminum tris(2,6-diphenylphenoxide) (ATPH), and the heterogeneous metal-organic framework Cu3BTC2 (BTC = benzene-1,3,5-tricarboxylate). ATPH is a strong Lewis acid homogeneous catalyst with bulky ligands which provides very high selectivities for the desired stereoisomer (>99%). The performance of the catalysts was evaluated as a function of temperature, which revealed that a higher catalyst activity allows working at lower temperatures and improves the selectivity for isopulegol. The selectivity distribution is kinetically driven for ZnBr2 and ATPH. The theoretical selectivity distributions rely on the determination of an extensive set of diastereomeric transition states, for which the differences in free energy have been calculated using a complementary set of ab initio techniques. Given the sensitivity of the selectivity to small Gibbs free-energy differences, the agreement between experimental and theoretical selectivities is satisfactory. On basis of the obtained insights, rational design of new catalysts may be obtained. As proof of concept, the hypothetical Cu-3(BTC-(NO2)(3))(2) Lewis catalyst - in which each phenyl hydrogen of the BTC ligand is replaced by a nitro group - is predicted to be very selective. (C) 2013 Elsevier Inc. All rights reserved. |
Vermoortele, Frederik; Bueken, Bart; Bars, Gaelle Le; de Voorde, Ben Van; Vandichel, Matthias; Houthoofd, Kristof; Vimont, Alexandre; Daturi, Marco; Waroquier, Michel; Speybroeck, Veronique Van; Kirschhock, Christine; Vos, Dirk De E Synthesis Modulation as a Tool To Increase the Catalytic Activity of Metal-Organic Frameworks: The Unique Case of UiO-66(Zr) Journal Article JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 135 (31), pp. 11465-11468, 2013, ISSN: 0002-7863. @article{ISI:000323019400014, title = {Synthesis Modulation as a Tool To Increase the Catalytic Activity of Metal-Organic Frameworks: The Unique Case of UiO-66(Zr)}, author = {Frederik Vermoortele and Bart Bueken and Gaelle Le Bars and Ben Van de Voorde and Matthias Vandichel and Kristof Houthoofd and Alexandre Vimont and Marco Daturi and Michel Waroquier and Veronique Van Speybroeck and Christine Kirschhock and Dirk E De Vos}, doi = {10.1021/ja405078u}, issn = {0002-7863}, year = {2013}, date = {2013-08-01}, journal = {JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, volume = {135}, number = {31}, pages = {11465-11468}, abstract = {The catalytic activity of the zirconium terephthalate UiO-66(Zr) can be drastically increased by using a modulation approach. The combined use of trifluoroacetic acid and HCl during the synthesis results in a highly crystalline material, with partial substitution of terephthalates by trifluoroacetate. Thermal activation of the material leads not only to dehydroxylation of the hexanuclear Zr cluster but also to post-synthetic removal of the trifluoroacetate groups, resulting in a more open framework with a large number of open sites. Consequently, the material is a highly active catalyst for several Lewis acid catalyzed reactions.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The catalytic activity of the zirconium terephthalate UiO-66(Zr) can be drastically increased by using a modulation approach. The combined use of trifluoroacetic acid and HCl during the synthesis results in a highly crystalline material, with partial substitution of terephthalates by trifluoroacetate. Thermal activation of the material leads not only to dehydroxylation of the hexanuclear Zr cluster but also to post-synthetic removal of the trifluoroacetate groups, resulting in a more open framework with a large number of open sites. Consequently, the material is a highly active catalyst for several Lewis acid catalyzed reactions. |
Ghysels, An; Vanduyfhuys, Louis; Vandichel, Matthias; Waroquier, Michel; Speybroeck, Veronique Van; Smit, Berend On the Thermodynamics of Framework Breathing: A Free Energy Model for Gas Adsorption in MIL-53 Journal Article JOURNAL OF PHYSICAL CHEMISTRY C, 117 (22), pp. 11540-11554, 2013, ISSN: 1932-7447. @article{ISI:000320214800011, title = {On the Thermodynamics of Framework Breathing: A Free Energy Model for Gas Adsorption in MIL-53}, author = {An Ghysels and Louis Vanduyfhuys and Matthias Vandichel and Michel Waroquier and Veronique Van Speybroeck and Berend Smit}, doi = {10.1021/jp311601q}, issn = {1932-7447}, year = {2013}, date = {2013-06-01}, journal = {JOURNAL OF PHYSICAL CHEMISTRY C}, volume = {117}, number = {22}, pages = {11540-11554}, abstract = {When adsorbing guest molecules, the porous metal-organic framework MIL-53(Cr) may vary its cell parameters drastically while retaining its crystallinity. A first approach to the thermodynamic analysis of this ``framework breathing'' consists of comparing the osmotic potential in two distinct shapes only (large-pore and narrow-pore). In this paper, we propose a generic parametrized free energy model including three contributions: host free energy, guest-guest interactions, and host-guest interaction. Free energy landscapes may now be constructed scanning all shapes and any adsorbed amount of guest molecules. This allows us to determine which shapes are the most stable states for arbitrary combinations of experimental control parameters, such as the adsorbing gas chemical potential, the external pressure, and the temperature. The new model correctly reproduces the structural transitions along the CO2 and CH4 isotherms. Moreover, our model successfully explains the adsorption versus desorption hysteresis as a consequence of the creation, stabilization, destabilization, and disappearance of a second free energy minimum under the assumptions of a first-order phase transition and collective behavior. Our general thermodynamic description allows us to decouple the gas chemical potential mu and mechanical pressure P as two independent thermodynamic variables and predict the complete (mu, P) phase diagram for CO2 adsorption in MIL-53(Cr). The free energy model proposed here is an important step toward a general thermodynamics description of flexible metal-organic frameworks.}, keywords = {}, pubstate = {published}, tppubtype = {article} } When adsorbing guest molecules, the porous metal-organic framework MIL-53(Cr) may vary its cell parameters drastically while retaining its crystallinity. A first approach to the thermodynamic analysis of this ``framework breathing'' consists of comparing the osmotic potential in two distinct shapes only (large-pore and narrow-pore). In this paper, we propose a generic parametrized free energy model including three contributions: host free energy, guest-guest interactions, and host-guest interaction. Free energy landscapes may now be constructed scanning all shapes and any adsorbed amount of guest molecules. This allows us to determine which shapes are the most stable states for arbitrary combinations of experimental control parameters, such as the adsorbing gas chemical potential, the external pressure, and the temperature. The new model correctly reproduces the structural transitions along the CO2 and CH4 isotherms. Moreover, our model successfully explains the adsorption versus desorption hysteresis as a consequence of the creation, stabilization, destabilization, and disappearance of a second free energy minimum under the assumptions of a first-order phase transition and collective behavior. Our general thermodynamic description allows us to decouple the gas chemical potential mu and mechanical pressure P as two independent thermodynamic variables and predict the complete (mu, P) phase diagram for CO2 adsorption in MIL-53(Cr). The free energy model proposed here is an important step toward a general thermodynamics description of flexible metal-organic frameworks. |
Liu, Ying-Ya; Couck, Sarah; Vandichel, Matthias; Grzywa, Maciej; Leus, Karen; Biswas, Shyam; Vollmer, Dirk; Gascon, Jorge; Kapteijn, Freek; Denayer, Joeri F M; Waroquier, Michel; Speybroeck, Veronique Van; der Voort, Pascal Van New V-IV-Based Metal-Organic Framework Having Framework Flexibility and High CO2 Adsorption Capacity Journal Article INORGANIC CHEMISTRY, 52 (1), pp. 113-120, 2013, ISSN: 0020-1669. @article{ISI:000313220500016, title = {New V-IV-Based Metal-Organic Framework Having Framework Flexibility and High CO2 Adsorption Capacity}, author = {Ying-Ya Liu and Sarah Couck and Matthias Vandichel and Maciej Grzywa and Karen Leus and Shyam Biswas and Dirk Vollmer and Jorge Gascon and Freek Kapteijn and Joeri F M Denayer and Michel Waroquier and Veronique Van Speybroeck and Pascal Van der Voort}, doi = {10.1021/ic301338a}, issn = {0020-1669}, year = {2013}, date = {2013-01-01}, journal = {INORGANIC CHEMISTRY}, volume = {52}, number = {1}, pages = {113-120}, abstract = {A vanadium based metal organic framework (MOF), VO(BPDC) (BPDC2- = biphenyl-4,4'-dicarboxylate), adopting an expanded MIL-47 structure type, has been synthesized via solvothermal and microwave methods. Its structural and gas/vapor sorption properties have been studied. This compound displays a distinct breathing effect toward certain adsorptives at workable temperatures. The sorption isotherms of CO2 and CH4 indicate a different sorption behavior at specific temperatures. In situ synchrotron X-ray powder diffraction measurements and molecular simulations have been utilized to characterize the structural transition. The experimental measurements clearly suggest the existence of both narrow pore and large pore forms. A free energy profile along the pore angle was computationally determined for the empty host framework. Apart from a regular large pore and a regular narrow pore form, an overstretched narrow pore form has also been found. Additionally, a variety of spectroscopic techniques combined with N-2 adsorption/desorption isotherms measured at 77 K demonstrate that the existence of the mixed oxidation states V-III/V-IV in the titled MOF structure compared to pure V-IV increases the difficulty in triggering the flexibility of the framework.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A vanadium based metal organic framework (MOF), VO(BPDC) (BPDC2- = biphenyl-4,4'-dicarboxylate), adopting an expanded MIL-47 structure type, has been synthesized via solvothermal and microwave methods. Its structural and gas/vapor sorption properties have been studied. This compound displays a distinct breathing effect toward certain adsorptives at workable temperatures. The sorption isotherms of CO2 and CH4 indicate a different sorption behavior at specific temperatures. In situ synchrotron X-ray powder diffraction measurements and molecular simulations have been utilized to characterize the structural transition. The experimental measurements clearly suggest the existence of both narrow pore and large pore forms. A free energy profile along the pore angle was computationally determined for the empty host framework. Apart from a regular large pore and a regular narrow pore form, an overstretched narrow pore form has also been found. Additionally, a variety of spectroscopic techniques combined with N-2 adsorption/desorption isotherms measured at 77 K demonstrate that the existence of the mixed oxidation states V-III/V-IV in the titled MOF structure compared to pure V-IV increases the difficulty in triggering the flexibility of the framework. |
2012 |
Vandichel, Matthias; Leus, Karen; der Voort, Pascal Van; Waroquier, Michel; Speybroeck, Veronique Van Mechanistic insight into the cyclohexene epoxidation with VO(acac)(2) and tert-butyl hydroperoxide Journal Article JOURNAL OF CATALYSIS, 294 , pp. 1-18, 2012, ISSN: 0021-9517. @article{ISI:000309314500001, title = {Mechanistic insight into the cyclohexene epoxidation with VO(acac)(2) and tert-butyl hydroperoxide}, author = {Matthias Vandichel and Karen Leus and Pascal Van der Voort and Michel Waroquier and Veronique Van Speybroeck}, doi = {10.1016/j.jcat.2012.06.002}, issn = {0021-9517}, year = {2012}, date = {2012-10-01}, journal = {JOURNAL OF CATALYSIS}, volume = {294}, pages = {1-18}, abstract = {The epoxidation reaction of cyclohexene is investigated for the catalytic system vanadyl acetylacetonate (VO(acac)(2)) with tert-butyl hydroperoxide (TBHP) as oxidant with the aim to identify the most active species for epoxidation and to retrieve insight into the most plausible epoxidation mechanism. The reaction mixture is composed of various inactive and active complexes in which vanadium may either have oxidation state +IV or +V. Inactive species are activated with TBHP to form active complexes. After reaction with cyclohexene, each active species transforms back into an inactive complex that may be reactivated again. The reaction mixture is quite complex containing hydroxyl, acetyl acetonate, acetate, or a tert-butoxide anion as ligands, and thus, various ligand exchange reactions may occur among active and inactive complexes. Also, radical decomposition reactions allow transforming V+IV to V+V species. To obtain insight into the most abundant active complexes, each of previous transformation steps has been modeled through thermodynamic equilibrium steps. To unravel the nature of the most plausible epoxidation mechanism, first principle chemical kinetics calculations have been performed on all proposed epoxidation pathways. Our results allow to conclude that the concerted Sharpless mechanism is the preferred reaction mechanism and that alkylperoxo species V+IVO(L)(OOtBu) and V+VO(L-1)(L-2)(OOtBu) species are most abundant. At the onset of the catalytic cycle, vanadium +IV species may play an active role, but as the reaction proceeds, reaction mechanisms that involve vanadium +V species are preferred as the acetyl acetonate is readily oxidized. Additionally, an experimental IR and kinetic study has been performed to give a qualitative composition of the reaction mixture and to obtain experimental kinetic data for comparison with our theoretical values. The agreement between theory and experiment is satisfactory. (C) 2012 Elsevier Inc. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The epoxidation reaction of cyclohexene is investigated for the catalytic system vanadyl acetylacetonate (VO(acac)(2)) with tert-butyl hydroperoxide (TBHP) as oxidant with the aim to identify the most active species for epoxidation and to retrieve insight into the most plausible epoxidation mechanism. The reaction mixture is composed of various inactive and active complexes in which vanadium may either have oxidation state +IV or +V. Inactive species are activated with TBHP to form active complexes. After reaction with cyclohexene, each active species transforms back into an inactive complex that may be reactivated again. The reaction mixture is quite complex containing hydroxyl, acetyl acetonate, acetate, or a tert-butoxide anion as ligands, and thus, various ligand exchange reactions may occur among active and inactive complexes. Also, radical decomposition reactions allow transforming V+IV to V+V species. To obtain insight into the most abundant active complexes, each of previous transformation steps has been modeled through thermodynamic equilibrium steps. To unravel the nature of the most plausible epoxidation mechanism, first principle chemical kinetics calculations have been performed on all proposed epoxidation pathways. Our results allow to conclude that the concerted Sharpless mechanism is the preferred reaction mechanism and that alkylperoxo species V+IVO(L)(OOtBu) and V+VO(L-1)(L-2)(OOtBu) species are most abundant. At the onset of the catalytic cycle, vanadium +IV species may play an active role, but as the reaction proceeds, reaction mechanisms that involve vanadium +V species are preferred as the acetyl acetonate is readily oxidized. Additionally, an experimental IR and kinetic study has been performed to give a qualitative composition of the reaction mixture and to obtain experimental kinetic data for comparison with our theoretical values. The agreement between theory and experiment is satisfactory. (C) 2012 Elsevier Inc. All rights reserved. |
Vanduyfhuys, L; Verstraelen, T; Vandichel, M; Waroquier, M; Speybroeck, Van V Ab Initio Parametrized Force Field for the Flexible Metal-Organic Framework MIL-53(Al) Journal Article JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 8 (9), pp. 3217-3231, 2012, ISSN: 1549-9618. @article{ISI:000308830700026, title = {Ab Initio Parametrized Force Field for the Flexible Metal-Organic Framework MIL-53(Al)}, author = {L Vanduyfhuys and T Verstraelen and M Vandichel and M Waroquier and V Van Speybroeck}, doi = {10.1021/ct300172m}, issn = {1549-9618}, year = {2012}, date = {2012-09-01}, journal = {JOURNAL OF CHEMICAL THEORY AND COMPUTATION}, volume = {8}, number = {9}, pages = {3217-3231}, abstract = {A force field is proposed for the flexible metal-organic framework MIL-53(Al), which is calibrated using density functional theory calculations on nonperiodic clusters. The force field has three main contributions: an electrostatic term based on atomic charges derived with a modified Hirshfeld-I method, a van der Waals (vdW) term with parameters taken from the MM3 model, and a valence force field whose parameters were estimated with a new methodology that uses the gradients and Hessian matrix elements retrieved from nonperiodic cluster calculations. The new force field predicts geometries and cell parameters that compare well with the experimental values both for the large and narrow pore phases. The energy profile along the breathing mode of the empty material reveals the existence of two minima, which confirms the intrinsic bistable behavior of the MIL-53. Even without the stimulus of external guest molecules, the material may transform from the large pore (lp) to the narrow pore (np) phase [Liu et al. J. Am. Chem. Soc. 2008, 120, 11813]. The relative stability of the two phases critically depends on the vdW parameters, and the MM3 dispersion interaction has the tendency to overstabilize the np phase.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A force field is proposed for the flexible metal-organic framework MIL-53(Al), which is calibrated using density functional theory calculations on nonperiodic clusters. The force field has three main contributions: an electrostatic term based on atomic charges derived with a modified Hirshfeld-I method, a van der Waals (vdW) term with parameters taken from the MM3 model, and a valence force field whose parameters were estimated with a new methodology that uses the gradients and Hessian matrix elements retrieved from nonperiodic cluster calculations. The new force field predicts geometries and cell parameters that compare well with the experimental values both for the large and narrow pore phases. The energy profile along the breathing mode of the empty material reveals the existence of two minima, which confirms the intrinsic bistable behavior of the MIL-53. Even without the stimulus of external guest molecules, the material may transform from the large pore (lp) to the narrow pore (np) phase [Liu et al. J. Am. Chem. Soc. 2008, 120, 11813]. The relative stability of the two phases critically depends on the vdW parameters, and the MM3 dispersion interaction has the tendency to overstabilize the np phase. |
Ghysels, An; Vandichel, Matthias; Verstraelen, Toon; van der Veen, Monique A; Vos, Dirk De E; Waroquier, Michel; Speybroeck, Veronique Van Host-guest and guest-guest interactions between xylene isomers confined in the MIL-47(V) pore system Journal Article THEORETICAL CHEMISTRY ACCOUNTS, 131 (7), 2012, ISSN: 1432-881X. @article{ISI:000307274300002, title = {Host-guest and guest-guest interactions between xylene isomers confined in the MIL-47(V) pore system}, author = {An Ghysels and Matthias Vandichel and Toon Verstraelen and Monique A van der Veen and Dirk E De Vos and Michel Waroquier and Veronique Van Speybroeck}, doi = {10.1007/s00214-012-1234-7}, issn = {1432-881X}, year = {2012}, date = {2012-07-01}, journal = {THEORETICAL CHEMISTRY ACCOUNTS}, volume = {131}, number = {7}, abstract = {The porous MIL-47 material shows a selective adsorption behavior for para-, ortho-, and meta-isomers of xylenes, making the material a serious candidate for separation applications. The origin of the selectivity lies in the differences in interactions (energetic) and confining (entropic). This paper investigates the xylene-framework interactions and the xylene-xylene interactions with quantum mechanical calculations, using a dispersion-corrected density functional and periodic boundary conditions to describe the crystal. First, the strength and geometrical characteristics of the optimal xylene-xylene interactions are quantified by studying the pure and mixed pairs in gas phase. An extended set of initial structures is created and optimized to sample as many relative orientations and distances as possible. Next, the pairs are brought in the pores of MIL-47. The interaction with the terephthalic linkers and other xylenes increases the stacking energy in gas phase (-31.7 kJ/mol per pair) by roughly a factor four in the fully loaded state (-58.3 kJ/mol per xylene). Our decomposition of the adsorption energy shows various trends in the contributing xylene-xylene interactions. The absence of a significant difference in energetics between the isomers indicates that entropic effects must be mainly responsible for the separation behavior.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The porous MIL-47 material shows a selective adsorption behavior for para-, ortho-, and meta-isomers of xylenes, making the material a serious candidate for separation applications. The origin of the selectivity lies in the differences in interactions (energetic) and confining (entropic). This paper investigates the xylene-framework interactions and the xylene-xylene interactions with quantum mechanical calculations, using a dispersion-corrected density functional and periodic boundary conditions to describe the crystal. First, the strength and geometrical characteristics of the optimal xylene-xylene interactions are quantified by studying the pure and mixed pairs in gas phase. An extended set of initial structures is created and optimized to sample as many relative orientations and distances as possible. Next, the pairs are brought in the pores of MIL-47. The interaction with the terephthalic linkers and other xylenes increases the stacking energy in gas phase (-31.7 kJ/mol per pair) by roughly a factor four in the fully loaded state (-58.3 kJ/mol per xylene). Our decomposition of the adsorption energy shows various trends in the contributing xylene-xylene interactions. The absence of a significant difference in energetics between the isomers indicates that entropic effects must be mainly responsible for the separation behavior. |
der Mynsbrugge, Jeroen Van; Hemelsoet, Karen; Vandichel, Matthias; Waroquier, Michel; Speybroeck, Veronique Van Efficient Approach for the Computational Study of Alcohol and Nitrile Adsorption in H-ZSM-5 Journal Article JOURNAL OF PHYSICAL CHEMISTRY C, 116 (9), pp. 5499-5508, 2012, ISSN: 1932-7447. @article{ISI:000301315700028, title = {Efficient Approach for the Computational Study of Alcohol and Nitrile Adsorption in H-ZSM-5}, author = {Jeroen Van der Mynsbrugge and Karen Hemelsoet and Matthias Vandichel and Michel Waroquier and Veronique Van Speybroeck}, doi = {10.1021/jp2123828}, issn = {1932-7447}, year = {2012}, date = {2012-03-01}, journal = {JOURNAL OF PHYSICAL CHEMISTRY C}, volume = {116}, number = {9}, pages = {5499-5508}, abstract = {Since many industrially important processes start with the adsorption of guest molecules inside the pores of an acidic zeolite catalyst, a proper estimate of the adsorption enthalpy is of paramount importance. In this contribution, we report ab initio calculations on the adsorption of water, alcohols, and nitriles at the bridging Bronsted sites of H-ZSM-5, using both cluster and periodic models to account for the zeolite environment. Stabilization of the adsorption complexes results from hydrogen bonding between the guest molecule and the framework, as well as from embedding, i.e., van der Waals interactions with the pore walls. Large-cluster calculations with different DFT methods, in particular B3LYP(-D), PBE(-D), M062X(-D), and omega B97X-D, are tested for their ability to reproduce the experimental heats of adsorption available in the literature (J. Phys. Chem. B 1997, 101, 3811-3817). A proper account of dispersion interactions is found to be crucial to describe the experimental trend across a series of adsorbates of increasing size, i.e., an increase in adsorption enthalpy by 10-15 kJ/mol for each additional carbon atom. The extended-cluster model is shown to offer an attractive alternative to periodic simulations on the entire H-ZSM-5 unit cell, resulting in virtually identical final adsorption enthalpies. Comparing calculated stretch frequencies of the zeolite acid sites and the adsorbate functional groups with experimental IR data additionally confirms that the cluster approach provides an appropriate representation of the adsorption complexes.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Since many industrially important processes start with the adsorption of guest molecules inside the pores of an acidic zeolite catalyst, a proper estimate of the adsorption enthalpy is of paramount importance. In this contribution, we report ab initio calculations on the adsorption of water, alcohols, and nitriles at the bridging Bronsted sites of H-ZSM-5, using both cluster and periodic models to account for the zeolite environment. Stabilization of the adsorption complexes results from hydrogen bonding between the guest molecule and the framework, as well as from embedding, i.e., van der Waals interactions with the pore walls. Large-cluster calculations with different DFT methods, in particular B3LYP(-D), PBE(-D), M062X(-D), and omega B97X-D, are tested for their ability to reproduce the experimental heats of adsorption available in the literature (J. Phys. Chem. B 1997, 101, 3811-3817). A proper account of dispersion interactions is found to be crucial to describe the experimental trend across a series of adsorbates of increasing size, i.e., an increase in adsorption enthalpy by 10-15 kJ/mol for each additional carbon atom. The extended-cluster model is shown to offer an attractive alternative to periodic simulations on the entire H-ZSM-5 unit cell, resulting in virtually identical final adsorption enthalpies. Comparing calculated stretch frequencies of the zeolite acid sites and the adsorbate functional groups with experimental IR data additionally confirms that the cluster approach provides an appropriate representation of the adsorption complexes. |
Vermoortele, Frederik; Vandichel, Matthias; de Voorde, Ben Van; Ameloot, Rob; Waroquier, Michel; Speybroeck, Veronique Van; Vos, Dirk De E Electronic Effects of Linker Substitution on Lewis Acid Catalysis with Metal-Organic Frameworks Journal Article ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 51 (20), pp. 4887-4890, 2012, ISSN: 1433-7851. @article{ISI:000303925200019, title = {Electronic Effects of Linker Substitution on Lewis Acid Catalysis with Metal-Organic Frameworks}, author = {Frederik Vermoortele and Matthias Vandichel and Ben Van de Voorde and Rob Ameloot and Michel Waroquier and Veronique Van Speybroeck and Dirk E De Vos}, doi = {10.1002/anie.201108565}, issn = {1433-7851}, year = {2012}, date = {2012-01-01}, journal = {ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, volume = {51}, number = {20}, pages = {4887-4890}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Leus, Karen; Vandichel, Matthias; Liu, Ying-Ya; Muylaert, Ilke; Musschoot, Jan; Pyl, Steven; Vrielinck, Henk; Callens, Freddy; Marin, Guy B; Detavernier, Christophe; Wiper, Paul V; Khimyak, Yaroslav Z; Waroquier, Michel; Speybroeck, Veronique Van; der Voort, Pascal Van The coordinatively saturated vanadium MIL-47 as a low leaching heterogeneous catalyst in the oxidation of cyclohexene Journal Article JOURNAL OF CATALYSIS, 285 (1), pp. 196-207, 2012, ISSN: 0021-9517. @article{ISI:000300074300022, title = {The coordinatively saturated vanadium MIL-47 as a low leaching heterogeneous catalyst in the oxidation of cyclohexene}, author = {Karen Leus and Matthias Vandichel and Ying-Ya Liu and Ilke Muylaert and Jan Musschoot and Steven Pyl and Henk Vrielinck and Freddy Callens and Guy B Marin and Christophe Detavernier and Paul V Wiper and Yaroslav Z Khimyak and Michel Waroquier and Veronique Van Speybroeck and Pascal Van der Voort}, doi = {10.1016/j.jcat.2011.09.014}, issn = {0021-9517}, year = {2012}, date = {2012-01-01}, journal = {JOURNAL OF CATALYSIS}, volume = {285}, number = {1}, pages = {196-207}, abstract = {A Metal Organic Framework, containing coordinatively saturated sites linked together by terephthalic linkers (V-MIL-47), is evaluated as a catalyst in the epoxidation of cyclohexene. Different solvents and conditions are tested and compared. If the oxidant TBHP is dissolved in water, a significant leaching of V-species into the solution is observed, and also radical pathways are prominently operative leading to the formation of an adduct between the peroxide and cyclohexene. If, however, the oxidant is dissolved in decane, leaching is negligible and the structural integrity of the V-MIL-47 is maintained during successive runs. The selectivity toward the epoxide is very high in these circumstances. Extensive computational modeling is performed to show that several reaction cycles are possible. EPR and NMR measurements confirm that at least two parallel catalytic cycles are co-existing: one with V+IV sites and one with pre-oxidized V+V sites, and this is in complete agreement with the theoretical predictions. (C) 2011 Elsevier Inc. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A Metal Organic Framework, containing coordinatively saturated sites linked together by terephthalic linkers (V-MIL-47), is evaluated as a catalyst in the epoxidation of cyclohexene. Different solvents and conditions are tested and compared. If the oxidant TBHP is dissolved in water, a significant leaching of V-species into the solution is observed, and also radical pathways are prominently operative leading to the formation of an adduct between the peroxide and cyclohexene. If, however, the oxidant is dissolved in decane, leaching is negligible and the structural integrity of the V-MIL-47 is maintained during successive runs. The selectivity toward the epoxide is very high in these circumstances. Extensive computational modeling is performed to show that several reaction cycles are possible. EPR and NMR measurements confirm that at least two parallel catalytic cycles are co-existing: one with V+IV sites and one with pre-oxidized V+V sites, and this is in complete agreement with the theoretical predictions. (C) 2011 Elsevier Inc. All rights reserved. |
Leus, Karen; Couck, Sarah; Vandichel, Matthias; Vanhaelewyn, Gauthier; Liu, Ying-Ya; Marin, Guy B; Driessche, Isabel Van; Depla, Diederik; Waroquier, Michel; Speybroeck, Veronique Van; Denayer, Joeri F M; Voort, Pascal Van Der Synthesis, characterization and sorption properties of NH2-MIL-47 Journal Article PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 14 (44), pp. 15562-15570, 2012, ISSN: 1463-9076. @article{ISI:000310153300037, title = {Synthesis, characterization and sorption properties of NH2-MIL-47}, author = {Karen Leus and Sarah Couck and Matthias Vandichel and Gauthier Vanhaelewyn and Ying-Ya Liu and Guy B Marin and Isabel Van Driessche and Diederik Depla and Michel Waroquier and Veronique Van Speybroeck and Joeri F M Denayer and Pascal Van Der Voort}, doi = {10.1039/c2cp42137b}, issn = {1463-9076}, year = {2012}, date = {2012-01-01}, journal = {PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, volume = {14}, number = {44}, pages = {15562-15570}, abstract = {An amino functionalized vanadium-containing Metal Organic Framework, NH2-MIL-47, has been synthesized by a hydrothermal reaction in an autoclave. Alternatively, a synthesis route via microwave enhanced irradiation has been optimized to accelerate the synthesis. The NH2-MIL-47 exhibits the same topology as MIL-47, in which the V center is octahedrally coordinated. After an exchange procedure in DMF the V+III center is oxidized to V+IV, which is confirmed by EPR and XPS measurements. The CO2 and CH4 adsorption properties have been evaluated and compared to MIL-47, showing that both MOFs have an almost similar adsorption capacity and affinity for CO2. DFT-based molecular modeling calculations were performed to obtain more insight into the adsorption positions for CO2 in NH2-MIL-47. Furthermore our calculated adsorption enthalpies agree well with the experimental values.}, keywords = {}, pubstate = {published}, tppubtype = {article} } An amino functionalized vanadium-containing Metal Organic Framework, NH2-MIL-47, has been synthesized by a hydrothermal reaction in an autoclave. Alternatively, a synthesis route via microwave enhanced irradiation has been optimized to accelerate the synthesis. The NH2-MIL-47 exhibits the same topology as MIL-47, in which the V center is octahedrally coordinated. After an exchange procedure in DMF the V+III center is oxidized to V+IV, which is confirmed by EPR and XPS measurements. The CO2 and CH4 adsorption properties have been evaluated and compared to MIL-47, showing that both MOFs have an almost similar adsorption capacity and affinity for CO2. DFT-based molecular modeling calculations were performed to obtain more insight into the adsorption positions for CO2 in NH2-MIL-47. Furthermore our calculated adsorption enthalpies agree well with the experimental values. |
2011 |
Speybroeck, Veronique Van; der Mynsbrugge, Jeroen Van; Vandichel, Matthias; Hemelsoet, Karen; Lesthaeghe, David; Ghysels, An; Marin, Guy B; Waroquier, Michel First Principle Kinetic Studies of Zeolite-Catalyzed Methylation Reactions Journal Article JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133 (4), pp. 888-899, 2011, ISSN: 0002-7863. @article{ISI:000287295300051, title = {First Principle Kinetic Studies of Zeolite-Catalyzed Methylation Reactions}, author = {Veronique Van Speybroeck and Jeroen Van der Mynsbrugge and Matthias Vandichel and Karen Hemelsoet and David Lesthaeghe and An Ghysels and Guy B Marin and Michel Waroquier}, doi = {10.1021/ja1073992}, issn = {0002-7863}, year = {2011}, date = {2011-02-01}, journal = {JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, volume = {133}, number = {4}, pages = {888-899}, abstract = {Methylations of ethene, propene, and butene by methanol over the acidic microporous H-ZSM-5 catalyst are studied by means of state of the art computational techniques, to derive Arrhenius plots and rate constants from first principles that can directly be compared with the experimental data. For these key elementary reactions in the methanol to hydrocarbons (MTH) process, direct kinetic data became available only recently [J. Catal. 2005, 224, 115-123; J. Catal. 2005, 234, 385-400]. At 350 degrees C, apparent activation energies of 103, 69, and 45 kJ/mol and rate constants of 2.6 x 10(-4), 4.5 x 10(-3), and 1.3 x 10(-2) mol/(g h mbar) for ethene, propene, and butene were ;derived, giving following relative ratios for methylation k(ethene)/k(propene)/k(butene) = 1:17:50. In this work, rate constants including pre-exponential factors are calculated which give very good agreement with the experimental data: apparent activation energies of 94, 62, and 37 kJ/mol for ethene, propene, and butene are found, and relative ratios of methylation k(ethene)/k(propene)/k(butene) = 1:23:763. The entropies of gas phase alkenes are underestimated in the harmonic oscillator approximation due to the occurrence of internal rotations. These low vibrational modes were substituted by manually constructed partition functions. Overall, the absolute reaction rates can be calculated with near chemical accuracy, and qualitative trends are very well reproduced. In addition, the proposed scheme is computationally very efficient and constitutes significant progress in kinetic modeling of reactions in heterogeneous catalysis.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Methylations of ethene, propene, and butene by methanol over the acidic microporous H-ZSM-5 catalyst are studied by means of state of the art computational techniques, to derive Arrhenius plots and rate constants from first principles that can directly be compared with the experimental data. For these key elementary reactions in the methanol to hydrocarbons (MTH) process, direct kinetic data became available only recently [J. Catal. 2005, 224, 115-123; J. Catal. 2005, 234, 385-400]. At 350 degrees C, apparent activation energies of 103, 69, and 45 kJ/mol and rate constants of 2.6 x 10(-4), 4.5 x 10(-3), and 1.3 x 10(-2) mol/(g h mbar) for ethene, propene, and butene were ;derived, giving following relative ratios for methylation k(ethene)/k(propene)/k(butene) = 1:17:50. In this work, rate constants including pre-exponential factors are calculated which give very good agreement with the experimental data: apparent activation energies of 94, 62, and 37 kJ/mol for ethene, propene, and butene are found, and relative ratios of methylation k(ethene)/k(propene)/k(butene) = 1:23:763. The entropies of gas phase alkenes are underestimated in the harmonic oscillator approximation due to the occurrence of internal rotations. These low vibrational modes were substituted by manually constructed partition functions. Overall, the absolute reaction rates can be calculated with near chemical accuracy, and qualitative trends are very well reproduced. In addition, the proposed scheme is computationally very efficient and constitutes significant progress in kinetic modeling of reactions in heterogeneous catalysis. |
Lesthaeghe, David; der Mynsbrugge, Jeroen Van; Vandichel, Matthias; Waroquier, Michel; Speybroeck, Veronique Van Full Theoretical Cycle for both Ethene and Propene Formation during Methanol-to-Olefin Conversion in H-ZSM-5 Journal Article CHEMCATCHEM, 3 (1), pp. 208-212, 2011, ISSN: 1867-3880. @article{ISI:000285888500026, title = {Full Theoretical Cycle for both Ethene and Propene Formation during Methanol-to-Olefin Conversion in H-ZSM-5}, author = {David Lesthaeghe and Jeroen Van der Mynsbrugge and Matthias Vandichel and Michel Waroquier and Veronique Van Speybroeck}, doi = {10.1002/cctc.201000286}, issn = {1867-3880}, year = {2011}, date = {2011-01-01}, journal = {CHEMCATCHEM}, volume = {3}, number = {1}, pages = {208-212}, abstract = {The methanol-to-olefin (MTO) process, catalyzed by acidic zeolites such as H-ZSM-5, provides an increasingly important alternative to the production of light olefins from crude oil. However, the various mechanistic proposals for methanol-to-olefin conversion have been strongly disputed for the past several decades. This work provides theoretical evidence that the experimentally suggested `alkene cycle', part of a co-catalytic hydrocarbon pool, offers a viable path to the production of both propene and ethene, in stark contrast to the often-proposed direct mechanisms. This specific proposal hinges on repeated methylation reactions of alkenes, starting from propene, which occur easily within the zeolite environment. Subsequent cracking steps regenerate the original propene molecule, while also forming new propene and ethene molecules as primary products. Because the host framework stabilizes intermediate carbenium ions, isomerization and de-protonation reactions are extremely fast. Combined with earlier joint experimental and theoretical work on polymethylbenzenes as active hydrocarbon pool species, it is clear that, in zeolite H-ZSM-5, multiple parallel and interlinked routes operate on a competitive basis.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The methanol-to-olefin (MTO) process, catalyzed by acidic zeolites such as H-ZSM-5, provides an increasingly important alternative to the production of light olefins from crude oil. However, the various mechanistic proposals for methanol-to-olefin conversion have been strongly disputed for the past several decades. This work provides theoretical evidence that the experimentally suggested `alkene cycle', part of a co-catalytic hydrocarbon pool, offers a viable path to the production of both propene and ethene, in stark contrast to the often-proposed direct mechanisms. This specific proposal hinges on repeated methylation reactions of alkenes, starting from propene, which occur easily within the zeolite environment. Subsequent cracking steps regenerate the original propene molecule, while also forming new propene and ethene molecules as primary products. Because the host framework stabilizes intermediate carbenium ions, isomerization and de-protonation reactions are extremely fast. Combined with earlier joint experimental and theoretical work on polymethylbenzenes as active hydrocarbon pool species, it is clear that, in zeolite H-ZSM-5, multiple parallel and interlinked routes operate on a competitive basis. |
2010 |
Vandichel, Matthias; Lesthaeghe, David; der Mynsbrugge, Jeroen Van; Waroquier, Michel; Speybroeck, Veronique Van Assembly of cyclic hydrocarbons from ethene and propene in acid zeolite catalysis to produce active catalytic sites for MTO conversion Journal Article JOURNAL OF CATALYSIS, 271 (1), pp. 67-78, 2010, ISSN: 0021-9517. @article{ISI:000277217500008, title = {Assembly of cyclic hydrocarbons from ethene and propene in acid zeolite catalysis to produce active catalytic sites for MTO conversion}, author = {Matthias Vandichel and David Lesthaeghe and Jeroen Van der Mynsbrugge and Michel Waroquier and Veronique Van Speybroeck}, doi = {10.1016/j.jcat.2010.02.001}, issn = {0021-9517}, year = {2010}, date = {2010-04-01}, journal = {JOURNAL OF CATALYSIS}, volume = {271}, number = {1}, pages = {67-78}, abstract = {The formation of cyclic hydrocarbons from smaller building blocks such as ethene and propene is investigated in protonated ZSM-5, using a 2-layered ONIOM(B3LYP/6-31+g(d):HF/6-31+g(d)) approach and an additional Grimme-type van der Waals dispersion correction term to account for the long-range dispersion interactions. These cyclic species form precursors for active hydrocarbon pool species and play a key role in activating the acidic zeolite host for successful methanol-to-olefin (MTO) conversion. Starting from trace amounts of ethene and propene that are formed during an initial induction period or during the active phase, dimerization reactions allow for rapid chain growth. The products of these reactions can be neutral alkenes, framework-bound alkoxide species or intermediate carbenium ions, depending on the zeolite environment taken into account. On the basis of rate constants for successive reaction steps, a viable route toward cyclization is proposed, which starts from the formation of a framework-bound propoxide from propene, followed by dimerization with an additional propene molecule to form the 2-hexyl carbenium ion which finally undergoes ring closure to yield methylcyclopentane. This cyclic species in turn forms a precursor for either an active hydrocarbon pool compound or for deactivating coke deposit. (C) 2010 Elsevier Inc. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The formation of cyclic hydrocarbons from smaller building blocks such as ethene and propene is investigated in protonated ZSM-5, using a 2-layered ONIOM(B3LYP/6-31+g(d):HF/6-31+g(d)) approach and an additional Grimme-type van der Waals dispersion correction term to account for the long-range dispersion interactions. These cyclic species form precursors for active hydrocarbon pool species and play a key role in activating the acidic zeolite host for successful methanol-to-olefin (MTO) conversion. Starting from trace amounts of ethene and propene that are formed during an initial induction period or during the active phase, dimerization reactions allow for rapid chain growth. The products of these reactions can be neutral alkenes, framework-bound alkoxide species or intermediate carbenium ions, depending on the zeolite environment taken into account. On the basis of rate constants for successive reaction steps, a viable route toward cyclization is proposed, which starts from the formation of a framework-bound propoxide from propene, followed by dimerization with an additional propene molecule to form the 2-hexyl carbenium ion which finally undergoes ring closure to yield methylcyclopentane. This cyclic species in turn forms a precursor for either an active hydrocarbon pool compound or for deactivating coke deposit. (C) 2010 Elsevier Inc. All rights reserved. |
Leus, Karen; Muylaert, Ilke; Vandichel, Matthias; Marin, Guy B; Waroquier, Michel; Speybroeck, Veronique Van; der Voort, Pascal Van The remarkable catalytic activity of the saturated metal organic framework V-MIL-47 in the cyclohexene oxidation Journal Article CHEMICAL COMMUNICATIONS, 46 (28), pp. 5085-5087, 2010, ISSN: 1359-7345. @article{ISI:000279565500010, title = {The remarkable catalytic activity of the saturated metal organic framework V-MIL-47 in the cyclohexene oxidation}, author = {Karen Leus and Ilke Muylaert and Matthias Vandichel and Guy B Marin and Michel Waroquier and Veronique Van Speybroeck and Pascal Van der Voort}, doi = {10.1039/c0cc01506g}, issn = {1359-7345}, year = {2010}, date = {2010-01-01}, journal = {CHEMICAL COMMUNICATIONS}, volume = {46}, number = {28}, pages = {5085-5087}, abstract = {The remarkable catalytic activity of the saturated metal organic framework MIL-47 in the epoxidation of cyclohexene is elucidated by means of both experimental results and theoretical calculations.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The remarkable catalytic activity of the saturated metal organic framework MIL-47 in the epoxidation of cyclohexene is elucidated by means of both experimental results and theoretical calculations. |
2009 |
Hemelsoet, Karen; Nollet, Arno; Vandichel, Matthias; Lesthaeghe, David; Speybroeck, Veronique Van; Waroquier, Michel The Effect of Confined Space on the Growth of Naphthalenic Species in a Chabazite-Type Catalyst: A Molecular Modeling Study Journal Article CHEMCATCHEM, 1 (3), pp. 373-378, 2009, ISSN: 1867-3880. @article{ISI:000274154100006, title = {The Effect of Confined Space on the Growth of Naphthalenic Species in a Chabazite-Type Catalyst: A Molecular Modeling Study}, author = {Karen Hemelsoet and Arno Nollet and Matthias Vandichel and David Lesthaeghe and Veronique Van Speybroeck and Michel Waroquier}, doi = {10.1002/cctc.200900208}, issn = {1867-3880}, year = {2009}, date = {2009-11-01}, journal = {CHEMCATCHEM}, volume = {1}, number = {3}, pages = {373-378}, abstract = {Methylation reactions of naphthalenic species over the acidic microporous zeolite with chabazite topology have been investigated by means of two-layered ab initio computations. Large cluster results combined with van der Waals contributions provide thermodynamic and kinetic results of successive methylation steps. The growth of fused bicyclic species is important as these can act as hydrocarbon pool species within the methanol-to-olefin (MTO) process, but ultimately leads to the deactivation of the catalyst. The influence of the confined space of the zeolite pore on the resulting transition state or product shape selectivity is investigated in detail.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Methylation reactions of naphthalenic species over the acidic microporous zeolite with chabazite topology have been investigated by means of two-layered ab initio computations. Large cluster results combined with van der Waals contributions provide thermodynamic and kinetic results of successive methylation steps. The growth of fused bicyclic species is important as these can act as hydrocarbon pool species within the methanol-to-olefin (MTO) process, but ultimately leads to the deactivation of the catalyst. The influence of the confined space of the zeolite pore on the resulting transition state or product shape selectivity is investigated in detail. |
