Methane Activation in Gold Cation-Exchanged Zeolites: A DFT Study
Methane Activation in Gold Cation-Exchanged Zeolites: A DFT Study
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DOI：
10.1021/cs200653q
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发表时间：
2012-04
期刊：
影响因子：
12.9
通讯作者：
S. Wannakao;Chompunuch Warakulwit;Kanokwan Kongpatpanich;M. Probst;J. Limtrakul
中科院分区：
文献类型：
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作者：
S. Wannakao;Chompunuch Warakulwit;Kanokwan Kongpatpanich;M. Probst;J. Limtrakul
甲烷的活化在实验室化学合成和大规模工业过程中引起了极大的兴趣。我们用密度泛函理论研究了甲烷在真空和不同类型沸石中对Au~+和Au~(2+)离子的C-H键断裂。采用了密度泛函M06-L和6-31G(d，p)基组，因为这个水平的理论对于过渡金属体系来说已经被证明是相当精确和负担得起的。我们考察了四种工业上重要的催化剂，ZSM-5，FAU，FER和MCM-22，每个都有特定的骨架拓扑结构，关于它们对甲烷活化的性能。ZSM-5结构中阳离子中心的双配位特性提供了比FAU结构更高的活性，其阳离子中心具有3倍的配位。由于结构约束的影响，Au-ZSM-5催化剂的反应活化能低于未加Au+离子的反应活化能(13.2vs21.3kcal/mol)。
Activation of methane has attracted a great deal of interest in laboratory chemical synthesis and in large-scale industrial processes. We performed density functional theory studies to investigate the C–H bond breaking of methane on Au+ and Au2+ ions in vacuum and inside different types of zeolites. The density functional M06-L and the 6-31G(d,p) basis set were employed as this level of theory had already been shown to be reasonably accurate and affordable for transition metal systems. We investigated four industrially important catalysts, ZSM-5, FAU, FER, and MCM-22, each with a particular framework topology, with respect to their performance for methane activation. The bicoordinated character of the cationic site in the ZSM-5 structure provides a higher activity than the FAU structure with a 3-fold coordination of its cationic site. The activation energy of the reaction catalyzed by Au-ZSM-5 is lower than the one with the bare Au+ cation (13.2 vs 21.3 kcal/mol) because of the structural constraint impos...