G.B. Marin

Ti-functionalized NH2-MIL-47: an effective and stable epoxidation catalyst

K. Leus, G. Vanhaelewyn, T. Bogaerts, Y-Y Liu, F. Esquivel, F. Callens, G.B. Marin, V. Van Speybroeck, H. Vrielinck, P. Van der Voort
Catalysis Today
208, 97-105


In this paper, we describe the post-functionalization of a V-containing Metal-organic framework with TiO(acac)2 to create a bimetallic oxidation catalyst. The catalytic performance of this V/Ti-MOF was examined for the oxidation of cyclohexene using molecular oxygen as oxidant in combination with cyclohexanecarboxaldehyde as co-oxidant. A significantly higher cyclohexene conversion was observed for the bimetallic catalyst compared to the non-functionalized material. Moreover, the catalyst could be recycled at least 3 times without loss of activity and stability. No detectable leaching of V or Ti was noted. Electron paramagnetic resonance measurements were performed to monitor the fraction of V-ions in the catalyst in the +IV valence state. A reduction of this fraction by ∼17% after oxidation catalysis is observed, in agreement with the generally accepted mechanism for this type of reaction.

Synthesis, characterization and sorption properties of NH2-MIL-47

K. Leus, S. Couck, M. Vandichel, G. Vanhaelewyn, Y-Y Liu, G.B. Marin, I. Van Driessche, D. Depla, M. Waroquier, V. Van Speybroeck, J.F.M. Denayer, P. Van der Voort
Physical Chemistry Chemical Physics (PCCP)
14, 15562–15570


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.

A coordinative saturated vanadium containing metal organic framework that shows a remarkable catalytic activity

K. Leus, I. Muylaert, V. Van Speybroeck, G.B. Marin, P. Van der Voort
Studies in Surface Science and Catalysis
175, 329-332


A completely saturated Metal Organic Framework, MIL-47 was synthesized and tested for its catalytic performance in the oxidation of cyclohexene with tert-butyl hydroperoxide as oxidant. The catalyst was compared to several reference catalysts: namely VAPO-5, supported VOx/SiO2 and the homogeneous catalyst VO(acac)2. MIL-47 shows a remarkable catalytic activity and preserves its crystalline structure and surface area after a catalytic run. Furthermore MIL-47 exhibits a very high activity in successive runs.

Theoretical Insights on Methylbenzene Side-Chain Growth in ZSM-5 Zeolites for Methanol-to-Olefin Conversion

D. Lesthaeghe, A. Horré, M. Waroquier, G.B. Marin, V. Van Speybroeck
Chemistry - A European Journal
15 (41), 10803–10808


The key step in the conversion of methane to polyolefins is the catalytic conversion of methanol to light olefins. The most recent formulations of a reaction mechanism for this process are based on the idea of a complex hydrocarbon-pool network, in which certain organic species in the zeolite pores are methylated and from which light olefins are eliminated. Two major mechanisms have been proposed to date—the paring mechanism and the side-chain mechanism—recently joined by a third, the alkene mechanism. Recently we succeeded in simulating a full catalytic cycle for the first of these in ZSM-5, with inclusion of the zeolite framework and contents. In this paper, we will investigate crucial reaction steps of the second proposal (the side-chain route) using both small and large zeolite cluster models of ZSM-5. The deprotonation step, which forms an exocyclic double bond, depends crucially on the number and positioning of the other methyl groups but also on steric effects that are typical for the zeolite lattice. Because of steric considerations, we find exocyclic bond formation in the ortho position to the geminal methyl group to be more favourable than exocyclic bond formation in the para position. The side-chain growth proceeds relatively easily but the major bottleneck is identified as subsequent de-alkylation to produce ethene. These results suggest that the current formulation of the side-chain route in ZSM-5 may actually be a deactivating route to coke precursors rather than an active ethene-producing hydrocarbon-pool route. Other routes may be operating in alternative zeotype materials like the silico-aluminophosphate SAPO-34.

First Principles Based Group Additive Values for the Gas Phase Standard Entropy and Heat Capacity of Hydrocarbons and Hydrocarbon Radicals

M. Sabbe, F. De Vleeschouwer, M-F. Reyniers, M. Waroquier, G.B. Marin
Journal of Physical Chemistry A
112 (47), 12235-12251


In this work a complete and consistent set of 95 Benson group additive values (GAVs) for standard entropies S° and heat capacities Cp° of hydrocarbons and hydrocarbon radicals is presented. These GAVs include 46 groups, among which 25 radical groups, which, to the best of our knowledge, have not been reported before. The GAVs have been determined from a set of B3LYP/6-311G(d,p) ideal gas statistical thermodynamics values for 265 species, consistently with previously reported GAVs for standard enthalpies of formation. One-dimensional hindered rotor corrections for all internal rotations are included. The computational methodology has been compared to experimental entropies (298 K) for 39 species, with a mean absolute deviation (MAD) between experiment and calculation of 1.2 J mol−1 K−1, and to 46 experimental heat capacities (298 K) with a resulting MAD = 1.8 J mol−1 K−1. The constructed database allowed evaluation of corrections on S° and Cp° for non-nearest-neighbor effects, which have not been determined previously. The group additive model predicts the S° and Cp° within 5 J mol−1 K−1 of the ab initio values for 11 of the 14 molecules of the test set, corresponding to an acceptable maximal deviation of a factor of 1.6 on the equilibrium coefficient. The obtained GAVs can be applied for the prediction of S° and Cp° for a wide range of hydrocarbons and hydrocarbon radicals. The constructed database also allowed determination of a large set of hydrogen bond increments, which can be useful for the prediction of radical thermochemistry.

Carbon-centered radical addition and beta-scission reactions: Modeling of activation energies and pre-exponential factors

M. Sabbe, M-F. Reyniers, V. Van Speybroeck, M. Waroquier, G.B. Marin
9 (1), 124-140


A consistent set of group additive values Delta GAV degrees for 46 groups is derived, allowing the calculation of rate coefficients for hydrocarbon radical additions and beta-scission reactions. A database of 51 rate coefficients based on CBS-QB3 calculations with corrections for hindered internal rotation was used as training set. The results of this computational method agree well with experimentally observed rate coefficients with a mean factor of deviation of 3, as benchmarked on a set of nine reactions. The temperature dependence on the resulting Delta GAV degrees s in the broad range of 300-1300K is limited to +/- 4.5 kJmol(-1) on activation energies and to +/- 0.4 on logA (A: pre-exponential factor) for 90% of the groups. Validation of the Delta GAV degrees s was performed for a test set of 13 reactions. In the absence of severe steric hindrance and resonance effects in the transition state, the rate coefficients predicted by group additivity are within a factor of 3 of the CBS-QB3 ab initio rate coefficients for more than 90% of the reactions in the test set. It can thus be expected that in most cases the GA method performs even better than standard DFT calculations for which a deviation factor of 10 is generally considered to be acceptable.

Open Access version available at UGent repository

Using elementary reactions to model growth processes of polyaromatic hydrocarbons under pyrolysis conditions of light feedstocks

K. Hemelsoet, V. Van Speybroeck, K.M. Van Geem, G.B. Marin, M. Waroquier
Molecular Simulation
34 (2) ,193-199


Density functional theory results are presented for elementary steps leading to coke growth within a steam cracking unit. The discussed pathway starts from toluene and ultimately, 1-methylnaphthalene is formed. In order to find the rate determining step for coke formation, the pseudo first-order rate coefficients of the various steps are compared taking into account the concentrations of diverse coke precursors. The influence of the polyaromatic environment is studied for a large set of methylated polycyclic aromatic molecules, by means of carbon–hydrogen bond dissociation enthalpy values. Subsequent hydrogen abstraction reactions at the methylated polyaromatics, by a methyl radical, are also examined. The abstraction is found to preferentially occur at the larger systems and is in general faster compared to abstractions at the analogous non-methylated species.

The Rise and Fall of Direct Mechanisms in Methanol-to-Olefin Catalysis:  An Overview of Theoretical Contributions

D. Lesthaeghe, V. Van Speybroeck, G.B. Marin, M. Waroquier
Industrial & Engineering Chemistry Research
46 (26), 8832-8838


Over the past 30 years, the methanol-to-olefin (MTO) process on acidic zeolites has been subject to a vast number of studies from both industrial and academic researchers, leading to numerous controversies regarding the most probable reaction mechanism. Improvement of computational facilities during the past decade led to a sudden boost of theoretical contributions that, when considered individually, all seemed to provide reasonable evidence for partial pathways of the commonly proposed direct mechanisms. Not only the reactions suggested by experimental studies were investigated, but in addition novel potential routes were discovered by theoreticians as well. However, when all of the individual reactions scattered throughout the literature were recently combined, theoretically obtained rate coefficients turned out to show the exact opposite, that is, the complete failure of the direct mechanisms to produce ethylene from methanol only. In this paper, we give a detailed overview of the theoretical contributions that initially supported the direct mechanism proposal, but which finally culminated in its demise.

Density Functional Theory Study of Free-Radical Polymerization of Acrylates and Methacrylates:  Structure−Reactivity Relationship

I. Değirmenci, D. Avci, V. Aviyente, K. Van Cauter, V. Van Speybroeck, G.B. Marin, M. Waroquier
40 (26), 9590–9602


Radical polymerization processes occur through a complex network of many different reactions. It is well-known that the polymerization rate is directly related to the monomer structure. The experimental polymerizability behavior is expressed as kp/kt1/2, where kp is the rate coefficient of propagation and kt is the rate coefficient of termination. In this study, the reactivity of a series of acrylates and methacrylates is modeled in order to understand the effect of the pendant group size, the polarity of a pendant group, and the nature of the pendant group (linear vs cyclic) on their polymerizability. The geometries and frequencies are calculated with the B3LYP/6-31+G(d) methodology whereas the energetics and kinetics of these monomers have been studied using the two-component BMK/6-311+G(3df,2p)//B3LYP/6-31+G(d) level of theory. For rotations about forming/breaking bonds in the transition state, an uncoupled scheme for internal rotations has been applied with potentials determined at the B3LYP/6-31+G(d) level. Generally the rate constants for propagation kp mimic the qualitative polymerization trend of the monomers modeled and can be used with confidence in predicting the polymerizability behavior of acrylates. However in the case of 2-dimethylaminoethyl acrylate, chain transfer is found to play a major role in inhibiting the polymerization. On the other hand, the disproportionation reaction turns out to be too slow to be taken into consideration as a termination reaction.


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