A core-shell structured Zn/SiO2@ZSM-5 catalyst: Preparation and enhanced catalytic properties in methane co-aromatization with propane

A core-shell structured Zn/SiO2@ZSM-5 catalyst was prepared by a hydrothermal coating method, and its physicochemical properties and catalytic performance in methane co-aromatization with propane were studied using a conventional solid catalyst (Zn/ZSM-5) as the comparison. Results revealed that methane was activated on Zn sites to form a large number of Zn methyl species and then incorporated during the aromatic formation process to promote the formation of aromatics. At a space velocity of 3600 mL g−1 h−1 and the reaction temperature of 550 ℃, the methane, propane conversion and the aromatics selectivity of Zn/SiO2@ZSM-5 catalyst were 7.9 %, 95.9 % and 88.1 %, respectively, which were higher than those of Zn/ZSM-5 catalyst by 2.8 %, 6.7 % and 6.8 %, respectively. The unique reaction pathway of core (Zn/SiO2, Zn sites)-shell (ZSM-5, acid sites) was mainly responsible for the superior performance in methane co-aromatization with propane. Meanwhile, the core-shell structured Zn/SiO2@ZSM-5 catalyst aroused the formation of distinct micro-macroporous system, which facilitated quick diffusion of desired products out of the intraframework channels and inhibited the formation of carbon deposits. These features of Zn/SiO2@ZSM-5 catalyst granted it superb diffusion ability and unique core-shell structure, which greatly enhanced the methane, propane conversion and aromatic selectivity together with a preeminent catalytic stability.