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.