B/Al/Ga-MOR分子筛催化甲醇/二甲醚羰基化反应机理的理论计算研究  

Theoretical calculation study on the reaction mechanism of methanol/dimethyl ether carbonylation catalyzed by the B/Al/Ga-MOR zeolites

作　　者：任鹏宇 刘卓 权燕红[2] 郭军军 马宏 武建兵 王永钊[1] REN Pengyu;LIU Zhuo;QUAN Yanhong;GUO Junjun;MA Hong;WU Jianbing;WANG Yongzhao(Engineering Research Center of Ministry of Education for Fine Chemicals,School of Chemistry and Chemical Engineering,Shanxi University,Taiyuan 030006,China;Taiyuan University of Technology,Key Laboratory of Coal Science and Technology,Ministry of Education,Shanxi Research Institute for Clean Energy Tsinghua University,Taiyuan 030024,China;Shanxi Lu'an Carbon One Chemical Co.,Ltd.,Changzhi 046100,China)

机构地区：[1]山西大学化学化工学院精细化学品教育部工程研究中心,山西太原030006 [2]太原理工大学煤科学与技术教育部重点实验室清华大学山西清洁能源研究院,山西太原030024 [3]山西潞安碳一化工有限公司,山西长治046100

出　　处：《燃料化学学报（中英文）》2024年第3期323-334,共12页Journal of Fuel Chemistry and Technology

基　　金：国家自然科学基金(22072079,22302115);山西省基础研究计划(202303021221056);太原理工大学煤科学与技术教育部重点实验室开放基金(MKX202103)资助。

摘　　要：采用DFT计算比较分析了B、Al和Ga分别同晶取代MOR分子筛八元环侧袋T3位点及十二元环孔道T4位点时甲醇及二甲醚羰基化反应机制的共性及差异。研究发现,CO插入甲氧基生成乙酰基的反应遵循S_(N)2机制,且为羰基化反应过程中的决速步;473 K下,无论甲醇或二甲醚为原料,生成的乙酰基更倾向于与甲醇中的CH3O作用生成乙酸甲酯;T3位点具有更好的羰基化择形性,而T4位点上更倾向于发生由三甲基氧鎓离子生成芳烃导致催化剂失活的副反应。与Al-MOR相比,在T3位点引入B和Ga会导致羰基化反应能垒的升高,降低其催化性能;而在T4位点引入B和Ga(尤其是B)则可大幅提升其生成三甲基氧鎓离子的能垒,抑制芳烃生成过程,提升催化剂稳定性。本工作有助于认识MOR分子筛不同孔道内酸性位点发生同晶取代时催化羰基化反应机制的差异,为调控设计高效MOR沸石催化剂提供一定的理论支撑。The reaction mechanism of methanol/dimethyl ether(DME)carbonylation catalyzed by isomorphously substituted B-,Al-,and Ga-MOR zeolites(B/Al/Ga-MOR)was comparatively investigated by the density functional theory(DFT)calculations.The commonalities and differences between methanol and dimethyl ether as the reactant as well as among various MOR zeolites in the catalytic reaction pathways were disclosed,where one Si atom was substituted by B,Al or Ga at the 8-ring side pockets T3 sites or the 12-ring channels T4 sites of MOR.The results indicate that the insertion of CO into methoxy group to form acetyl groups follows the S_(N)2 mechanism and is the rate-determining step in the carbonylation reactions.Under 473 K,either methanol or dimethyl ether is used as feedstock,the formed acetyl group prefers to interact with CH3O in methanol to form methyl acetate.The T3 sites show better carbonylation selectivity,whereas T4 sites display better trimethoxonium ions selectivity which favors the generation of aromatics and leads to the catalyst deactivation.Comparing with Al-MOR,the introduction of Ga and B at the T3 sites increases the free energy barriers of carbonylation,whereas the introduction of Ga and B in particular at the T4 sites can substantially increase the energy barriers of generating trimethyloxonium ions,which can effectively suppress the side reaction and improve the catalyst stability.This work contributes to the understanding of the catalytic roles of various acidic sites in different channels of the MOR zeolites and provides certain theoretical support for tailoring and designing efficient MOR zeolite catalysts for methanol/dimethyl ether carbonylation.

关 键 词：羰基化 甲醇 二甲醚 B/Al/Ga-MOR分子筛 DFT计算 反应机理 

分 类 号：O64[理学—物理化学]