Methylbenzene hydrocarbon pool in methanol-to-olefins conversion over zeolite H-ZSM-5
Methylbenzene hydrocarbon pool in methanol-to-olefins conversion over zeolite H-ZSM-5
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DOI：
10.1016/j.jcat.2015.10.001
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发表时间：
2015-12
影响因子：
7.3
通讯作者：
Chao Wang;Jun Xu;Guodong Qi;Yanjun Gong;Weiyu Wang;Pan Gao;Qiang Wang;Ningdong Feng;
中科院分区：
文献类型：
--
作者：
Chao Wang;Jun Xu;Guodong Qi;Yanjun Gong;Weiyu Wang;Pan Gao;Qiang Wang;Ningdong Feng;
研究了 H-ZSM-5 沸石上甲醇制烯烃 (MTO) 反应诱导期内甲苯 (MBs) 烃库的形成和反应性，揭示了 MBs 与乙烯和丙烯的机制联系。形成的MB的时间演变分析和12C/13C甲醇转换实验表明，在诱导期，较大的化合物例如tetraMB和pentaMB比它们的较轻的对应物例如p/m-diMB和triMB具有更高的反应性。通过将H-ZSM-5上捕获的MB的分布与乙烯和丙烯相关联，我们发现tetraMB和pentaMB有利于丙烯的形成，而p/m-diMB和triMB主要有助于乙烯的形成。在此关系的基础上，可以通过改变ZSM-5的硅铝比、反应温度和空速来调节捕获的MB的分布来控制烯烃（乙烯和丙烯）选择性。 MB 的反应性以及 MB 与烯烃的相关性也在稳态条件下得到了验证。通过使用原位固态核磁共振波谱观察关键的环戊烯基和五甲基苯正离子中间体，提出了一种将 MB 与乙烯和丙烯连接的配对机制。 P/M-diMB 和 triMB 产生乙基环戊烯基阳离子，然后分裂出乙烯，而 tetraMB 和 pentaMB 产生连接有丙基的中间体，最终产生丙烯。这项工作为 MTO 化学中的 MB 烃库提供了新的见解。
The formation and reactivity of a methylbenzenes (MBs) hydrocarbon pool in the induction period of the methanol-to-olefins (MTO) reaction over zeolite H-ZSM-5 was investigated and the mechanistic link of MBs to ethene and propene was revealed. Time evolution analysis of the formed MBs and12C/13C methanol-switching experiments indicate that in the induction period bulkier compounds such as tetraMB and pentaMB have higher reactivity than their lighter counterparts such as p/m-diMB and triMB. By correlating the distribution of MBs trapped on H-ZSM-5 with ethene and propene, we found that tetraMB and pentaMB favor the formation of propene, while p/m-diMB and triMB mainly contribute to the formation of ethene. On the basis of this relationship, the olefin (ethene and propene) selectivity can be controlled by regulating the distribution of trapped MBs by varying the silicon-to-aluminum ratio of ZSM-5, reaction temperature, and space velocity. The reactivity of MBs and the correlation of MBs with olefins were also verified under steady-state conditions. By observation of key cyclopentenyl and pentamethylbenzenium cation intermediates using in situ solid-state NMR spectroscopy, a paring mechanism was proposed to link MBs with ethene and propene. P/M-diMB and triMB produce ethylcyclopentenyl cations followed by splitting off of ethene, while tetraMB and pentaMB generate propyl-attached intermediates, which eventually produce propene. This work provides new insight into the MBs hydrocarbon pool in MTO chemistry.