Comparing alkene-mediated and formaldehyde-mediated diene formation routes in methanol-to-olefins catalysis in MFI and CHA
Comparing alkene-mediated and formaldehyde-mediated diene formation routes in methanol-to-olefins catalysis in MFI and CHA
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DOI：
10.1016/j.jcat.2021.05.010
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发表时间：
2021-06-12
影响因子：
7.3
通讯作者：
Hibbitts, David
中科院分区：
文献类型：
--
作者：
Kilburn, Lauren;DeLuca, Mykela;Hibbitts, David
本文采用密度泛函理论研究了MFI和CHA分子筛中烯烃和CH_2O介导的甲醇制烯烃（MTO）反应过程中二烯的生成。研究了在MTO过程中存在的C1-C4表面键合烷基的速率控制氢化物转移反应。在CH 2 O介导的途径中，表面结合的烷基和CH 3 OH之间的速率决定性氢转移最有利于叔丁基，其中在C-4：C-1烷基比例低至10（-10）（MFI中）和10（-6）时，氢转移速率超过甲基。在CHA中。在烯烃介导的途径中，氢化物转移最有利地在C4 H8和仲烷基之间进行以形成丁二烯，其中丙基-C4 H8（在MFI中）和仲丁基-C4 H8（在CHA中）氢化物转移在甲基-C4 H8上发生，当它们的相对表面浓度分别是甲基的10（-10）和10（-5）倍时。通常，一旦形成，C2+表面烷基是比CH 3-Z更好的氢化物受体，表明失活可能是由MTO产物形成的较大的表面结合烷基驱动的。(C)2021爱思唯尔公司All rights reserved.
This work uses DFT to investigate diene formation during methanol-to-olefins (MTO) via alkene-mediated and CH2O-mediated pathways in MFI and CHA zeolites. The rate controlling hydride transfer reactions were investigated with C-1-C-4 surface-bound alkyls present during MTO. In the CH2O-mediated pathway, rate-determining hydride transfer between surface-bound alkyl and CH3OH occurs most favorably with tert-butyl where rates of the hydride transfer exceed that of methyl at C-4:C-1 alkyl ratios as low as 10(-10) in MFI and 10(-6) in CHA. In the alkene-mediated route, hydride transfers proceed most favorably between C4H8 and secondary alkyls to form butadiene, where propyl-C4H8 (in MFI) and sec-butyl-C4H8 (in CHA) hydride transfers occur over methyl-C4H8 when their relative surface concentrations are 10(-10) and 10(-5) times that of methyl, respectively. Generally, once formed, C2+ surface alkyls are better hydride acceptors than CH3-Z, suggesting deactivation may be driven by larger surface-bound alkyls, formed by MTO products. (C) 2021 Elsevier Inc. All rights reserved.