Formation and Evolution of Methylcyclohexene in the Initial Period of Methanol to Olefins over H-ZSM-5
Formation and Evolution of Methylcyclohexene in the Initial Period of Methanol to Olefins over H-ZSM-5
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H-ZSM-5甲醇制烯烃初期甲基环己烯的形成与演化
DOI：
10.1021/acscatal.2c03410
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发表时间：
2022-09
期刊：
影响因子：
12.9
通讯作者：
Jianguo Wang
中科院分区：
文献类型：
--
作者：
Sheng Fan;Han Wang;Shipei He;Kai Yuan;Pengfei Wang;Junfen Li;Sen Wang;Zhangfeng Qin;Mei Dong;Weibin Fan;Jianguo Wang
甲醇转化为轻质烯烃（MTO）过程中反应中间体的识别并探讨其演化过程颇具挑战性，但对于揭示烃池（HCP）机理以及探索更高效的MTO催化剂具有重要意义。因此，我们想报告一下，通过瞬态脉冲实验、13C交叉极化/魔角旋转核磁共振（CP/MAS NMR）、气相色谱-质谱（GC-MS）和密度泛函理论（DFT）计算等多种措施，发现甲基环己烯（MCH）是H-ZSM-5上MTO初期的关键反应中间体。诱导阶段产生的早期烯烃（主要是乙烯和丙烯）可以通过低聚快速构建长链烯烃，并通过与甲醇脱氢的甲醛进行普林斯反应产生二烯。之后，通过二烯和单烯之间的狄尔斯-阿尔德（D-A）反应很容易形成MCH。与烯烃的低聚和环化相比，D-A反应在构建更大分子产物时表现出更高的活性和更低的能垒。 MCH具有高反应性，可以通过环收缩快速转化为甲基环戊烯（MCP），或通过氢化物转移和去质子化快速转化为甲苯（MB）；在低温下MCP的形成可能优先于MB的形成，因为前者的反应需要较低的能垒。因此，MCH作为连接MCP和MB的桥梁，对于MTO中初始HCP的建立起着至关重要的作用。这些发现有助于深入了解MTO反应机理，进而有利于MTO的进一步研究。
Identification of the reaction intermediates and probing into their evolution in the conversion of methanol to light olefins (MTO) are rather challenging but meaningful in unraveling the hydrocarbon pool (HCP) mechanism as well as in exploring more efficient catalysts in MTO. Hence, we would like to report a finding made in this regard that methylcyclohexene (MCH) is a crucial reaction intermediate in the initial period of MTO over H-ZSM-5 through various measures, including transient pulse experiment,13C cross-polarization/magic angle spinning nuclear magnetic resonance (CP/MAS NMR), gas chromatography–mass spectrometry (GC–MS), and density-functional theory (DFT) calculation. The early alkenes (mostly ethene and propene) produced in the induction stage can rapidly construct the long-chain alkenes through oligomerization and create dienes through the Prins reaction with formaldehyde from methanol dehydrogenation. After that, MCH is facilely formed via the Diels–Alder (D–A) reaction between dienes and monoenes. Compared with the oligomerization and cyclization of alkenes, the D–A reaction shows higher activity with a lower energy barrier in building larger molecule products. MCH is highly reactive and can be quickly transformed either into methylcyclopentene (MCP) via ring contraction or into methylbenzene (MB) via hydride transfer and deprotonations; the formation of MCP may take the priority over that of MB at a low temperature, as the former reaction needs a lower energy barrier. Accordingly, MCH acts as a bridge connecting MCP and MB and plays a vital role in the establishment of initial HCP in MTO. These findings should be helpful for an in-depth understanding of the MTO reaction mechanism and then benefit further research into MTO.
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