The Density Functional Theory Study Of The Mechanism Of The Conversion Of Methane To Ethane Over Zn/ZSM-5 Catalysts

Methane is the main component of the natural gas that can be used as energy and chemical materials. The product of combustion of methane and the methane are the greenhouse gas. Therefore, converting the methane to more valuable and cleaner substances attracts widespread attentions. Because of the chemical property of methane that is the the simplest alkane is very stable. Usually, people convert the methane to the syngas then convert it into other substances, but the method needs more energy.Currently, the study on the methane activation reaction is very hot and the catalysts that are used are also various. However, there are many problems. For instance, the catalytic efficiency of catalyst is low and easy to lose catalyst activity and the product is not easy to deal with. In recent years, researchers find that the metal-exchanged zeolites display a good catalytic activity on methane activation. Particularly, ZSM-5 zeolites catalyst can activate methane under the very mild reaction conditions. The present article studies the catalytic reaction mechanism that the ZSM-5 zeolite catalyst mixed by zinc how to catalyze the methane to produce the ethane.In this paper, Zn²⁺ and [ZnOZn]²⁺ are mixed respectively into the ZSM-5 zeolites, optimizing two different structures of metal-exchanged ZSM-5 zeolites catalyst. The method of ONIOM layered calculation is use to calculate the pathway of the methane activation. The following results are obtained. By examining the charge distribution of methane activation and the changes of molecular structure, the paper verifies the methane is activated according to the "alkyl" reaction mechanism. Zn / ZSM-5 zeolites catalyst can catalyze methane to ethane. The methane activation is relatively easier than the ethane generation, because the ethane generation reaction need more energy than the methane activation, so the reaction is not easy to occur. Zn2 + and [ZnOZn]²⁺ are mixed respectively into the ZSM-5 zeolite catalysts to catalyze the methane, then, they show the different energy barriers and [ZnOZn]²⁺ mixed ZSM-5 zeolites exhibit better catalytic activity. There are two oxygen skeletons at the T12 active site in the Zn / ZSM-5 zeolite catalyst that can accept the hydrogen ion of methane polarization.The different framework oxygen that accept ions of hydrogen, the different energy barrier of methane activation.