Coating mesoporous ZSM-5 by microporous silicalite-1 shell: Preparation and enhanced catalytic properties in methane co-aromatization with propane

A novel core-shell structured catalyst (Zn/[email protected]) with the microporous silicalite-1 shell and the mesoporous ZSM-5 core (Zn/MZSM-5) was prepared by the epitaxial recrystallization method using tetrapropylammonium hydroxide (TPAOH) as template. Multitechniques including XRD, TEM, N2 adsorption-desorption, XPS, 27Al NMR, IR, NH3-TPD, IG and ICP were employed to investigate the physicochemical properties of the core-shell [email protected] and the deactivation of carbon deposits. Results revealed that the diffusion capacities of [email protected] have been dramatically improved after the epitaxial growth of the silicalite-1 shell. In addition, the non-acidic silicalite-1 shell covering on Zn/MZSM-5 core could decrease the external Brønsted acid sites, and thus inhibit the formation of carbon deposits. Applying the protective shell increased the stability of the core-shell catalyst in comparison to Zn/MZSM-5 catalyst without the silicalite-1 shell. However, the overgrowth of the silicalite-1 shell extended the diffusion path of reactants and products, reducing the catalytic properties in methane co-aromatization with propane. In this sense, the controlled formation of desired thickness of the silicalite-1 shell around Zn/MZSM-5 core accounted for the enhanced catalytic properties.