Synthesis of core–shell structured TS-1@mesocarbon materials and their applications as a tandem catalyst

Abstract

Core–shell structured TS-1@mesocarbon (TS-1@MC) materials with mesoporous carbon as the shell and microporous TS-1 titanosilicate as the core were synthesized through a nanocasting and selective silica etching strategy. The faithful replica structure was constructed from the composite of TS-1@mesosilica and carbon when tetrapropylammonium hydroxide (TPAOH) was employed to selectively remove the amorphous mesosilica shell while the core zeolite crystal structure was not destroyed. In contrast, the protective effect was not seen when sodium hydroxide or hydrogen fluoride was employed as a silica-leaching agent. The obtained TS-1@MC had a bimodal pore structure consisting of 2.9 nm mesopores in the carbon shell and 0.51 nm micropores in the TS-1 core. Its specific surface area and total pore volume reached 883 m² g⁻¹ and 0.63 cm³ g⁻¹, respectively. TS-1@MC was used as the support to load palladium nanoparticles (Pd NPs) in the carbon shell. Having an average particle size of approximately 2 nm, the Pd NPs were highly dispersed and confined in the mesopores of the carbon shell. Pd/TS-1@MC thus obtained served as an efficient tandem catalyst in the direct epoxidation of propylene with hydrogen and oxygen.