Cooperativity between Al Sites Promotes Hydrogen Transfer and Carbon-Carbon Bond Formation upon Dimethyl Ether Activation on Alumina.
Cooperativity between Al Sites Promotes Hydrogen Transfer and Carbon-Carbon Bond Formation upon Dimethyl Ether Activation on Alumina.
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DOI：
10.1021/acscentsci.5b00226
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发表时间：
2015-09-23
影响因子：
18.2
通讯作者：
Sautet P
中科院分区：
文献类型：
--
作者：
Comas-Vives A;Valla M;Copéret C;Sautet P
甲醇制烯烃（MTO）工艺允许甲醇/二甲醚通过所谓的烃池机制在酸性沸石上转化为烯烃。然而，第一个碳-碳键的形成位置和机制仍然是一个有争议的问题。在这里，我们表明，刘易斯酸性铝位上的110面的γ-Al 2 O3可以很容易地激活二甲醚，产生甲烷，烯烃，和表面甲酸盐物种根据光谱研究结合计算方法。碳-碳形成步骤以及甲烷和表面甲酸盐的形成涉及瞬态氧鎓离子中间体，由表面甲氧基物种和相邻Al位点上的配位甲醇之间的氢转移产生。这些结果表明，酸性沸石中与氧化铝缔合的骨架外Al中心可以在第一碳-碳键的形成（工业MTO工艺的起始步骤）中发挥关键作用。氧化铝上相邻的刘易斯酸位点协同作用，通过H-转移活化二甲醚，产生CH 4和表面甲酸盐或烯烃和H2O。
The methanol-to-olefin (MTO) process allows the conversion of methanol/dimethyl ether into olefins on acidic zeolites via the so-called hydrocarbon pool mechanism. However, the site and mechanism of formation of the first carbon–carbon bond are still a matter of debate. Here, we show that the Lewis acidic Al sites on the 110 facet of γ-Al2O3 can readily activate dimethyl ether to yield CH4, alkenes, and surface formate species according to spectroscopic studies combined with a computational approach. The carbon–carbon forming step as well as the formation of methane and surface formate involves a transient oxonium ion intermediate, generated by a hydrogen transfer between surface methoxy species and coordinated methanol on adjacent Al sites. These results indicate that extra framework Al centers in acidic zeolites, which are associated with alumina, can play a key role in the formation of the first carbon–carbon bond, the initiation step of the industrial MTO process. Adjacent Lewis acid sites on alumina play in concert to activate dimethyl ether via H-transfer yielding CH4 and surface formate or olefins and H2O.