Insight into Dimethyl Ether Carbonylation Reaction over Mordenite Zeolite from in-Situ Solid-State NMR Spectroscopy
Insight into Dimethyl Ether Carbonylation Reaction over Mordenite Zeolite from in-Situ Solid-State NMR Spectroscopy
复制标题
通过原位固态核磁共振波谱深入了解丝光沸石上的二甲醚羰基化反应
DOI：
10.1021/jp400331m
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发表时间：
2013-03-21
影响因子：
3.7
通讯作者：
Deng, Feng
中科院分区：
文献类型：
--
作者：
Li, Bojie;Xu, Jun;Deng, Feng
用原位C-13固体核磁共振技术研究了423 ~ 573 K温度范围内H-丝光沸石（H-MOR）分子筛上二甲醚（DME）与CO的羰基化反应。在相同的条件下，在8元环（MR）和沸石的12-MR通道中分别监测反应。实验结果表明，8-MR和12-MR通道都能产生乙酸甲酯产物，但选择性有显著差异。在低反应温度下，表面乙酰物种（CH 3CO-）作为稳定的acylium阳离子被单独确定在8-MR通道，这是通过测量其特征化学位移各向异性（CSA）参数证实。此外，乙酰基物质的中间体作用通过其可与DME反应形成乙酸甲酯的事实得到证明。这证明了理论上提出的8-MR通道对乙酰基中间体的产生和稳定的特异性，乙酰基中间体被认为是羰基化反应的限速步骤。而在12-MR通道中，在反应过程中没有发现乙酰基中间体，并且有利于烃的形成。乙酰基中间体的不存在可能是12-MR通道生成乙酸甲酯产物的反应性较低的原因。
Carbonylation of dimethyl ether (DME) with CO over H-mordenite (H-MOR) zeolites from 423 to 573 K was studied by in-situ C-13 solid-state NMR spectroscopy. The reaction was monitored separately in the 8-membered ring (MR) and in the 12-MR channels of the zeolite under identical conditions. The experimental results indicated that both 8-MR and 12-MR channels were capable of producing methyl acetate product but with remarkably different selectivities. At low-reaction temperature, surface acetyl species (CH3CO-) as stabilized acylium cation was solely identified in the 8-MR channels, which was confirmed by measurement of its characteristic chemical shift anisotropy (CSA) parameters. Additionally, the intermediate role of the acetyl species was evidenced by the fact that it could react with DME to form methyl acetate. This demonstrated the theoretically proposed specificity of the 8-MR channels for generation and stabilization of the acetyl intermediate which was considered as the rate-limiting step of carbonylation reaction. While in the 12-MR channels, the acetyl intermediate was not found during the reaction, and formation of hydrocarbons was favored. The absence of acetyl intermediate might account for the lower reactivity of the 12-MR channels to generate methyl acetate product.