An ONIOM Study of Thiophene Cracking in a Brönsted Acidic Zeolite

An ONIOM study at B3LYP and M05-2X level was carried out to investigate thiophene cracking in a Brönsted acidic zeolite and the effect of the zeolite framework on the geometry, electronic structure, and energy of the intermediates. The zeolite framework stabilized positively charged transition states and lowered the reaction barriers. The newly developed M05-2X functional performed much better than the popular B3LYP functional for describing non-bonded interactions between the reactants and the zeolite framework, which gave more accurate electronic structures and energy barriers. The rate determining barrier was that for electrophilic aromatic substitution (122.4 kJ/mol), while the subsequent C-S bond dissociation has a lower barrier (75.5 kJ/mol).

摘要：采用 ONIOM 法研究了分子筛上噻吩的裂解反应, 考察了分子筛骨架环境对反应中各物种的几何构型、电荷分布以及整个反应的影响. 比较了 B3LYP 和 M05-2X 泛函的计算结果. 结果表明, 分子筛骨架可很好地稳定反应带电中间体, 促进了吸附分子的电荷分离, 从而使反应活化能降低. 与现在应用广泛的 B3LYP 泛函相比, 最近开发的 M05-2X 泛函能够更准确地描述反应物分子和分子筛骨架的相互作用, 计算得到的电荷分布和活化能也更为合理. 整个反应的决速步是亲电取代反应, 其活化能为 122.4 kJ/mol, 随后的 C–S 键解离活化能较低, 为 75.5 kJ/mol.

An ONIOM study at the B3LYP and M05-2X levels was carried out to investigate thiophene cracking in H-ZSM-5 and the effect of the zeolite framework on the geometry, electronic structure, and energy of the intermediates.Figure optionsDownload as PowerPoint slide