@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}