苯和甲醇在H-ZSM-5催化剂上甲基化的反应机理

发布时间：2018-03-29 23:03

本文选题：密度泛函理论　切入点：ONIOM　出处：《物理化学学报》2017年04期

【摘要】：采用"our own-N-layered integrated molecular orbital+molecular mechanics"(ONIOM)和密度泛函理论(DFT)结合的方法,在5T、12T、104T_9和104T_(12)H-ZSM-5模型中研究了苯和甲醇甲基化的分步和协同机理。描述了中间体物种和过渡态的结构。考察了H-ZSM-5催化剂Br?nsted(B)酸强度对苯和甲醇甲基化反应机理的影响。反应活化能结果表明,在B酸强度更强的H-ZSM-5催化剂上,苯和甲醇甲基化反应更容易发生,反应活化能更低。随着B酸强度增强,分步机理的反应活化能比协同机理的反应活化能降低的更多。B酸强度增强对分步机理更有利。当分步机理成为主导反应路径时,分步机理中甲醇脱水步骤生成的甲氧基中间体进一步生成大体积烃类的副反应会导致H-ZSM-5催化剂因积炭而失活。合理调变H-ZSM-5催化剂的酸强度对提高催化剂的催化活性和稳定性有重要意义。
[Abstract]:Using the method of "our own-N-layered integrated molecular orbital molecular mechanics" and density functional theory (DFT), the stepwise and synergistic mechanism of methylation of benzene and methanol was studied in the 5T ~ (12) T ~ (12) T ~ (10 ~ 4) T _ 9 and 104T_(12)H-ZSM-5 model. The structure of intermediate species and transition state was described. The effect of acid strength on the mechanism of methylation of benzene with methanol. The results of activation energy show that the methylation of benzene with methanol is easier and the activation energy of the reaction is lower with the increase of the strength of B acid on the H-ZSM-5 catalyst with higher strength of B acid. The activation energy of the stepwise mechanism is more favorable to the stepwise mechanism than that of the synergistic mechanism. The side reaction of methoxy intermediate produced by methanol dehydration step in the stepwise mechanism will lead to the deactivation of H-ZSM-5 catalyst due to carbon deposition. The modification of acid strength of H-ZSM-5 catalyst can improve the catalytic activity of the catalyst. Sex and stability are of great significance.
【作者单位】：辽宁科技学院冶金工程学院;大连理工大学化工学院精细化工国家重点实验室PSU-DUT联合能源研究中心;宾夕法尼亚州立大学能源与矿物工程系能源研究所PSU-DUT联合能源研究中心;
【基金】：辽宁省教育厅科学研究一般项目基金(L2014503) 辽宁省自然科学基金项目(201602403) 辽宁科技学院博士科研启动基金项目(1406B08) 国家自然科学基金项目(21503027)资助~~
【分类号】：O643.36

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