期刊
SOLID STATE NUCLEAR MAGNETIC RESONANCE
卷 35, 期 2, 页码 100-103出版社
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.ssnmr.2008.12.002
关键词
Isobutane; Alkane activation; C-H bond activation; In-situ NMR; Catalysis; Zeolite; Mechanism
资金
- American Chemical Society [PRF 46837-AC5]
H-1 solid-state NMR techniques have been used to simultaneously detect the reactivity of both catalyst and alkane reactant protons in an in-situ experimental design. Specifically, the activation of isobutane C-H bonds by the solid acid zeolite H-Beta is directly observed while the reaction is in progress, and the rate of proton transfer between the solid catalyst surface and gaseous isobutane is quantitatively measured using isotopic H-1/H-2 exchange methods. Arrhenius analysis of isothermal kinetic runs revealed an apparent activation barrier of 70 kJ/mole for the exchange process between isobutane and the 12-membered ring H-Beta, which exceeds our previously determined value of 57 kJ/mole for isobutane in the 10-membered ring H-ZSM-5 (JACS 2006, v. 128, p. 1848). Estimation of true activation energies using heat of adsorption data from the literature combined with the experimentally measured apparent E-a suggests that the true activation barrier differs by only 6-7 kJ/mole in the two catalysts. We discuss the possibility that subtle shape selectivity, or inverse shape selectivity, and lattice solvation differences between the two catalysts account for the enhanced solvation of the isobutane transition state in HZSM-5 compared to the larger channel H-Beta. In all experiments, the isobutane reagent was treated to eliminate any unsaturated impurities that might serve as initiators for carbenium-ion mechanisms, and the active catalyst was free of any organic contaminants that might serve as a source of unsaturated initiators. (C) 2009 Elsevier Inc. All rights reserved.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据