Mechanism of CH4 Activation on a Monomeric Zn2+-Ion Exchanged in MFI-Type Zeolite with a Specific Al Arrangement: Similarity to the Activation Site for H2

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• 作者：Akira Oda ; Hiroe Torigoe ; Atsushi Itadani ; Takahiro Ohkubo ; Takashi Yumura ; Hisayoshi Kobayashi ; Yasushige Kuroda
• 刊名：Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：September 26, 2013
• 年：2013
• 卷：117
• 期：38
• 页码：19525-19534
• 全文大小：488K
• 年卷期：v.117,no.38(September 26, 2013)
• ISSN：1932-7455

文摘

In this work, we used both experimental and density functional theory (DFT) calculation methods to examine the mechanism of CH₄ activation taking place on the Zn²⁺ ion exchanged MFI-type zeolite (ZnMFI). The heterolytic dissociation of CH₄ on ZnMFI around 300 K was observed experimentally, causing the appearance of IR bands at 3615, 2930, and 2892 cm^鈥?. The first band can be assigned to the OH stretching vibration associated with the formation of the Br酶nsted acid site and the latter to the C鈥揌 stretching modes ascribable to the 鈭抂ZnCH₃]⁺ species. Combining the IR spectroscopy with a DFT calculation, it is apparent that the heterolytic C鈥揌 bond dissociation of CH₄ has an activation energy of 15 kJ mol^鈥? and takes place on a monomeric Zn²⁺ at the M7S2 site. The M7S2 site has a specific Al arrangement in MFI and exhibits a pronounced reactivity for the H鈥揌 bond cleavage of H₂, even at room temperature. In addition, to our knowledge, we are the first to succeed in explaining the dissociation process of CH₄ by applying natural bond orbital (NBO) and interaction localized orbital (ILO) analyses to the present system; the donation interaction from the CH₄鈥撓?C鈥揌) orbital to the Zn鈥?s orbital triggers the cleavage of the C鈥揌 bond of CH₄ under mild conditions.