https://scholars.lib.ntu.edu.tw/handle/123456789/611501
標題: | Effects of Zeolite Structural Confinement on Adsorption Thermodynamics and Reaction Kinetics for Monomolecular Cracking and Dehydrogenation of n-Butane | 作者: | Janda A. Vlaisavljevich B. Lin L.-C. Smit B. Bell A.T. LI-CHIANG LIN |
關鍵字: | Adsorption;Butane;Cracks;Dehydrogenation;Enthalpy;Entropy;Equilibrium constants;Intelligent systems;Monte Carlo methods;Paraffins;Thermodynamics;Topology;Zeolites;Activation enthalpies;Adsorption equilibrium constants;Adsorption thermodynamics;Channel topology;Dehydrogenation of n-butane;Freedom of movement;Rate coefficients;Zeolite structure;Reaction kinetics;alkane;butane;hexane;proton;zeolite;adsorption;Article;catalyst;chemical reaction kinetics;dehydrogenation;enthalpy;entropy;equilibrium constant;Monte Carlo method;proton transport;thermodynamics;chemistry;computer simulation;hydrogenation;kinetics;X ray diffraction;Butanes;Computer Simulation;Hydrogenation;Kinetics;Monte Carlo Method;X-Ray Diffraction | 公開日期: | 2016 | 卷: | 138 | 期: | 14 | 起(迄)頁: | 4739-4756 | 來源出版物: | Journal of the American Chemical Society | 摘要: | The effects of zeolite structure on the kinetics of n-butane monomolecular cracking and dehydrogenation are investigated for eight zeolites differing in the topology of channels and cages. Monte Carlo simulations are used to calculate enthalpy and entropy changes for adsorption (ΔHads-H+ and ΔSads-H+) of gas-phase alkanes onto Br?nsted protons. These parameters are used to extract intrinsic activation enthalpies (ΔHint?), entropies (ΔSint?), and rate coefficients (kint) from measured data. As ΔSads-H+ decreases (i.e., as confinement increases), ΔHint? and ΔSint? for terminal cracking and dehydrogenation decrease for a given channel topology. These results, together with positive values observed for ΔSint?, indicate that the transition states for these reactions resemble products. For central cracking (an earlier transition state), ΔHint? is relatively constant, while ΔSint? increases as ΔSads-H+ decreases because less entropy is lost upon protonation of the alkane. Concurrently, selectivities to terminal cracking and dehydrogenation decrease relative to central cracking because ΔSint? decreases for the former reactions. Depending on channel topology, changes in the measured rate coefficients (kapp) with confinement are driven by changes in kint or by changes in the adsorption equilibrium constant (Kads-H+). Values of ΔSint? and ΔHint? are positively correlated, consistent with weaker interactions between the zeolite and transition state and with the greater freedom of movement of product fragments within more spacious pores. These results differ from earlier reports that ΔHint? and ΔSint? are structure-insensitive and that kapp is dominated by Kads-H+. They also suggest that ΔSads-H+ is a meaningful descriptor of confinement for zeolites having similar channel topologies. ? 2016 American Chemical Society. |
URI: | https://www.scopus.com/inward/record.uri?eid=2-s2.0-84964670716&doi=10.1021%2fjacs.5b11355&partnerID=40&md5=a1d8fe9e07707a3c2903964bf966300e https://scholars.lib.ntu.edu.tw/handle/123456789/611501 |
DOI: | 10.1021/jacs.5b11355 |
顯示於: | 化學工程學系 |
在 IR 系統中的文件,除了特別指名其著作權條款之外,均受到著作權保護,並且保留所有的權利。