Mechanistic insights into the catalytic role of various acid sites on ZSM-5 zeolite in the carbonylation of methanol and dimethyl ether
Mechanistic insights into the catalytic role of various acid sites on ZSM-5 zeolite in the carbonylation of methanol and dimethyl ether
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ZSM-5沸石上各种酸位在甲醇和二甲醚羰基化反应中催化作用的机理见解
DOI：
10.1039/c8cy00296g
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发表时间：
2018-06
影响因子：
5
通讯作者：
Wang Jianguo
中科院分区：
文献类型：
--
作者：
Wang Sen;Li Shiying;Zhang Li;Qin Zhangfeng;Chen Yanyan;Dong Mei;Li Junfen;Fan Weibin;Wang Jianguo
采用DFT-D计算和微动力学分析相结合的方法，研究了ZSM-5分子筛上位于直通道、正弦通道和交腔的不同酸位点在甲醇和二甲醚（DME）羰基化反应中的催化作用。结果表明，醋酸酯的形成优先于直道，而交叉腔中的酸性位点可能诱导甲醇和二甲醚转化为意想不到的副产物，从而导致ZSM-5催化剂的快速失活。羰基化过程中不同酸位的催化行为受其所在环境和周围骨架结构的强烈影响，而骨架结构又决定了空间约束和静电稳定效应。同时，二甲醚作为原料在直道中羰基化反应活性高于甲醇，有利于生成乙酸甲酯。因此，ZSM-5在羰基化过程中的催化活性和产物选择性可以通过有目的地调节酸位点的位置来精细调节。此外，由于亲核CH3+ -CO中间体和亲电Cu位点之间的强静电相互作用，将Cu加入ZSM-5沸石，特别是单核铜（Cu）种，可以进一步提高羰基化反应速率。这项工作有助于阐明ZSM-5上不同酸位的催化作用，以及活性Cu物质在羰基化反应中的性质，这对设计羰基化过程中高效的沸石催化剂有很大的好处。
The catalytic role of various acid sites located at the straight channel, sinusoidal channel and intersection cavity on ZSM-5 zeolite in the carbonylation of methanol and dimethyl ether (DME) was investigated through combined DFT-D calculation and micro-kinetic analysis. The results indicate that the formation of acetate takes priority in the straight channel, whereas the acid sites in the intersection cavity may induce the conversion of methanol and DME into unexpected by-products that lead to the rapid deactivation of the ZSM-5 catalyst. The catalytic behavior of various acid sites in carbonylation is strongly influenced by their local environment and the surrounding framework structure which determine the space confinement and electrostatic stabilization effects. Meanwhile, DME as feedstock shows a higher carbonylation activity than methanol in the straight channel, producing preferably methyl acetate. As a result, the catalytic activity and product selectivity of ZSM-5 in carbonylation can be finely tuned through purposely regulating the location of acid sites. Moreover, the carbonylation reaction rate can be further elevated through incorporating Cu into the ZSM-5 zeolites, especially mononuclear copper (Cu) species, due to the strong electrostatic interaction between the nucleophilic CH3+–CO intermediate and electrophilic Cu sites. This work helps to clarify the catalytic role of various acid sites on ZSM-5, as well as the nature of active Cu species in the carbonylation reaction, which is of great benefit to the design of efficient zeolite catalysts for the carbonylation process.
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