2008

Molecular Simulations of Zeolites: Adsorption, Diffusion, and Shape Selectivity

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B. Smit and T. L. M. Maesen, Molecular Simulations of Zeolites: Adsorption, Diffusion, and Shape Selectivity Chem. Rev. 108 (10), 4125 (2008) http://dx.doi.org/10.1021/cr8002642


Computer Simulation of Shape Selectivity Effects

Handbook of Heterogeneous Catalysis

B. Smit and T. L. M. Maesen, "Computer Simulation of Shape Selectivity Effects" in Handbook of heterogeneous catalysis, edited by G. Ertl, H. Knözinger, F. Schueth, and J. Weitkamp (Wiley-VCH, Weinheim; Chichester, 2008), Vol. 5, pp. 1676. http://dx.doi.org/10.1002/9783527610044.hetcat0091


Towards a molecular understanding of shape selectivity

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B. Smit and T. L. M. Maesen, Towards a molecular understanding of shape selectivity Nature 451 (7179), 671 (2008) http://dx.doi.org/10.1038/nature06552

Shape selectivity is a simple concept: the transformation of reactants into products depends on how the processed molecules fit the active site of the catalyst. Nature makes abundant use of this concept, in that enzymes usually process only very few molecules, which fit their active sites. Industry has also exploited shape selectivity in zeolite catalysis for almost 50 years, yet our mechanistic understanding remains rather limited. Here we review shape selectivity in zeolite catalysis, and argue that a simple thermodynamic analysis of the molecules adsorbed inside the zeolite pores can explain which products form and guide the identification of zeolite structures that are particularly suitable for desired catalytic applications.

Shape-selective n-alkane hydroconversion at exterior zeolite surfaces

T. L. M. Maesen, R. Krishna, J. M. van Baten, B. Smit, S. Calero, and J. M. C. Sanchez, Shape-selective n-alkane hydroconversion at exterior zeolite surfaces J. Catal. 256 (1), 95 (2008) http://dx.doi.org/10.1016/j.jcat.2008.03.004

A critical review of the adsorption and catalysis of n- and methylalkanes demonstrates that the interior surface of TON- and MTT-type zeolites dominates both adsorption and catalysis, and that the contribution from the exterior surface is negligible. For both n- and methylalkane isomers, the experimental Henry constants at the interior TON-type zeolite surface are more than an order of magnitude greater than those at the exterior surface. Molecular simulations on exclusively interior TON-type silica surface reproduce the adsorption isotherms of n- and methylalkane isomers remarkably well and suggest that even an isomer as bulky as 2,3-dimethylpentane could have access to the interior TON-type zeolite surface. Only the reference state used in solution thermodynamics affords an equitable comparison between internal and external surface thermodynamics. It indicates that methylalkanes adsorb in a structured fashion at the exterior TON-type zeolite surface when the interior surface is inaccessible. But the entropic penalty for this organized exterior surface “pore mouth” or “key-lock” adsorption is high, so that methylalkanes prefer adsorption at the interior surface when it is accessible. We speculate that CHA- and ERI-type sieves exhibit exterior surface catalysis in long n-alkane conversion, but the database remains too small to allow investigation of the full potential of shape selectivity in exterior zeolite surface catalysis.

A New United Atom Force Field for Adsorption of Alkenes in Zeolites

B. Liu, B. Smit, F. Rey, S. Valencia, and S. Calero, A New United Atom Force Field for Adsorption of Alkenes in Zeolites J. Phys. Chem. C. 112 (7), 2492 (2008) http://dx.doi.org/10.1021/jp075809d


A new united atom force field was developed that accurately describes the adsorption properties of linear alkenes in zeolites. The force field was specifically designed for use in the inhomogeneous system and therefore a truncated and shifted potential was used. With the determined force field, we performed a comparative study on the adsorption behaviors of ethene and propene in four pure-silica small-pore eight-membered-ring zeolites, CHA, DDR, ITE, and IHW (named Chabazite, DD3R, ITQ-3, and ITQ-32, respectively), characterized for their paraffin/olefin separation capability. The different macroscopic adsorption behaviors of alkenes in the four zeolites were elucidated and related to their structures with the microscopic information obtained from the molecular simulations providing useful information for further rational design of such zeolites with tailored properties.

Enhanced adsorption selectivity of hydrogen/methane mixtures in metal-organic frameworks with interpenetration: A molecular simulation study

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B. Liu, Q. Yang, C. Xue, C. Zhong, B. Chen, and B. Smit, Enhanced adsorption selectivity of hydrogen/methane mixtures in metal-organic frameworks with interpenetration: A molecular simulation study J. Phys. Chem. C 112 (26), 9854 (2008) http://dx.doi.org/10.1021/jp802343n


In this work a systematic molecular simulation study was performed to study the effect of interpenetration on gas mixture separation in metal−organic frameworks (MOFs). To do this, three pairs of isoreticular MOFs (IRMOFs) with and without interpenetration were adopted to compare their adsorption separation selectivity for CH4/H2 mixtures at room temperature. The results show that methane selectivity is greatly enhanced in the interpenetrated IRMOFs compared with their noninterpenetrated counterparts, due to the formation of additional small pores and adsorption sites by the interpenetration of frameworks. Furthermore, this work shows methane selectivity behavior is more complex in the former and selectivity differs largely in the different areas of the pores, attributed to the existence of various small pores of different sizes. In addition, the present work shows the ideal adsorbed solution theory is likely to be applicable to interpenetrated MOFs with complex structures.

Molecular simulation of hydrogen diffusion in interpenetrated metal-organic frameworks

Graphical abstract: Molecular simulation of hydrogen diffusion in interpenetrated metal–organic frameworks

B. Liu, Q. Y. Yang, C. Y. Xue, C. L. Zhong, and B. Smit, Molecular simulation of hydrogen diffusion in interpenetrated metal-organic frameworks Phys. Chem. Chem. Phys. 10 (22), 3244 (2008) http://dx.doi.org/10.1039/b801494a


In this work a combined molecular dynamics simulation and dynamically corrected transition-state theory (dcTST) study was performed to investigate the effect of interpenetration (catenation) on hydrogen diffusion in metal–organic frameworks (MOFs) as well as their relationships. The results on 10 isoreticular MOFs (IRMOFs) with and without interpenetration show that catenation can reduce hydrogen diffusivity by a factor of 2 to 3 at room temperature, and for the interpenetrated IRMOFs with multi-pores of different sizes, free volume can serve as a measure for hydrogen diffusivity: the bigger the free volume, the larger the hydrogen diffusivity. In addition, the present work shows that dcTST can directly reveal the influence of the MOF structure on hydrogen diffusivity, which is a powerful tool for providing a better understanding of the relationship between gas diffusivity and MOF structure.


Molecular simulations of lipid-mediated protein-protein interactions

F. J. M. de Meyer, M. Venturoli, and B. Smit, Molecular simulations of lipid-mediated protein-protein interactions Biophys. J. 95 (4), 1851 (2008) http://dx.doi.org/10.1529/biophysj.107.124164


Recent experimental results revealed that lipid-mediated interactions due to hydrophobic forces may be important in determining the protein topology after insertion in the membrane, in regulating the protein activity, in protein aggregation and in signal transduction. To gain insight into the lipid-mediated interactions between two intrinsic membrane proteins, we developed a mesoscopic model of a lipid bilayer with embedded proteins, which we studied with dissipative particle dynamics. Our calculations of the potential of mean force between transmembrane proteins show that hydrophobic forces drive long-range protein-protein interactions and that the nature of these interactions depends on the length of the protein hydrophobic segment, on the three-dimensional structure of the protein and on the properties of the lipid bilayer. To understand the nature of the computed potentials of mean force, the concept of hydrophilic shielding is introduced. The observed protein interactions are interpreted as resulting from the dynamic reorganization of the system to maintain an optimal hydrophilic shielding of the protein and lipid hydrophobic parts, within the constraint of the flexibility of the components. Our results could lead to a better understanding of several membrane processes in which protein interactions are involved.


© Berend Smit 2019