Shape-Selective Diffusion of Olefins in 8-Ring Solid Acid Microporous Zeolites

被引:76
作者
Ghysels, An [1 ]
Moors, Samuel L. C. [1 ]
Hemelsoet, Karen [1 ]
De Wispelaere, Kristof [1 ]
Waroquier, Michel [1 ]
Sastre, German [2 ]
Van Speybroeck, Veronique [1 ]
机构
[1] Univ Ghent, Ctr Mol Modeling, B-9052 Zwijnaarde, Belgium
[2] Univ Politecn Valencia, Inst Tecnol Quim UPV CSIC, E-46022 Valencia, Spain
基金
欧盟地平线“2020”; 欧洲研究理事会;
关键词
MOLECULAR-DYNAMICS SIMULATIONS; NEGATIVE THERMAL-EXPANSION; NMR SELF-DIFFUSION; HIGH-SILICA DDR; REACTION-MECHANISM; HYDROCARBON FORMATION; MODELING ADSORPTION; LOADING DEPENDENCE; LTA ZEOLITES; MTO REACTION;
D O I
10.1021/acs.jpcc.5b06010
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The diffusion of olefins through 8-ring solid acid microporous zeolites is investigated using molecular dynamics simulations techniques and using a newly developed flexible force field. Within the context of the methanol-to-olefin (MTO) process and the observed product distribution, knowledge of the diffusion paths is essential to obtain molecular level control over the process conditions. Eight-ring zeotype materials are favorably used for the MTO process as they give a selective product distribution toward low-carbon olefins. To investigate how composition, acidity, and flexibility influence the diffusion paths of ethene and propene, a series of isostructural aluminosilicates (zeolites) and silicoaluminophosphates (AlPOs and SAPOs) are investigated with and without randomly distributed acidic sites. Distinct variations in diffusion of ethene are observed in terms of temperature, composition, acidity, and topology (AEI, CHA, AFX). In general, diffusion of ethene is an activated process for which free energy barriers for individual rings may be determined. We observe ring-dependent diffusion behavior which cannot be described solely in terms of the composition and topology of the rings. A new descriptor had to be introduced, namely, the accessible window area (AWA), inspired by implicit solvation models of proteins and small molecules. The AWA may be determined throughout the molecular dynamics trajectories and correlates well with the number of ring crossings at the molecular level and the free energy barriers for ring crossings from one cage to the other. The overall observed diffusivity is determined by molecular characteristics of individual rings for which AWA is a proper descriptor. Temperature-induced changes in framework dynamics and diffusivity may be captured by following the new descriptor throughout the simulations.
引用
收藏
页码:23721 / 23734
页数:14
相关论文
共 75 条
[21]   The importance of various degrees of freedom in the theoretical study of the diffusion of methane in silicalite-1 [J].
Fritzsche, S ;
Wolfsberg, M ;
Haberlandt, R .
CHEMICAL PHYSICS, 2003, 289 (2-3) :321-333
[22]   The General Utility Lattice Program (GULP) [J].
Gale, JD ;
Rohl, AL .
MOLECULAR SIMULATION, 2003, 29 (05) :291-341
[23]   DERIVATION OF INTERATOMIC POTENTIALS FOR MICROPOROUS ALUMINOPHOSPHATES FROM THE STRUCTURE AND PROPERTIES OF BERLINITE [J].
GALE, JD ;
HENSON, NJ .
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS, 1994, 90 (20) :3175-3179
[24]   Analytical free energy minimization of silica polymorphs [J].
Gale, JD .
JOURNAL OF PHYSICAL CHEMISTRY B, 1998, 102 (28) :5423-5431
[25]   Modeling Adsorption and Self-Diffusion of Methane in LTA Zeolites: The Influence of Framework Flexibility [J].
Garcia-Sanchez, A. ;
Dubbeldam, D. ;
Calero, S. .
JOURNAL OF PHYSICAL CHEMISTRY C, 2010, 114 (35) :15068-15074
[26]   Diffusion of propane, propylene and isobutane in 13X zeolite by molecular dynamics [J].
Granato, Miguel A. ;
Jorge, Miguel ;
Vlugt, Thijs J. H. ;
Rodrigues, Alirio E. .
CHEMICAL ENGINEERING SCIENCE, 2010, 65 (09) :2656-2663
[27]   The mechanism of methanol to hydrocarbon catalysis [J].
Haw, JF ;
Song, WG ;
Marcus, DM ;
Nicholas, JB .
ACCOUNTS OF CHEMICAL RESEARCH, 2003, 36 (05) :317-326
[28]   PFG NMR self-diffusion of small hydrocarbons in high silica DDR, CHA and LTA structures [J].
Hedin, Niklas ;
DeMartin, Gregory J. ;
Roth, Wieslaw J. ;
Strohmaier, Karl G. ;
Reyes, Sebastian C. .
MICROPOROUS AND MESOPOROUS MATERIALS, 2008, 109 (1-3) :327-334
[29]   Unraveling the Reaction Mechanisms Governing Methanol-to-Olefins Catalysis by Theory and Experiment [J].
Hemelsoet, Karen ;
Van der Mynsbrugge, Jeroen ;
De Wispelaere, Kristof ;
Waroquier, Michel ;
Van Speybroeck, Veronique .
CHEMPHYSCHEM, 2013, 14 (08) :1526-1545
[30]   Experimental and theoretical IR study of methanol and ethanol conversion over H-SAPO-34 [J].
Hemelsoet, Karen ;
Ghysels, An ;
Mores, Davide ;
De Wispelaere, Kristof ;
Van Speybroeck, Veronique ;
Weckhuysen, Bert M. ;
Waroquier, Michel .
CATALYSIS TODAY, 2011, 177 (01) :12-24