A Well-Defined Core-Shell-Structured Capsule Catalyst for Direct Conversion of CO2 into Liquefied Petroleum Gas

A Pd/SiO2@S1@H-ZSM-5 capsule catalyst (Pd/SiO2-SZ) is fabricated through a dual-layer crystal growth method with an auxiliary hydrothermal reaction. The catalyst exhibits excellent selectivity to liquefied petroleum gas (LPG) in CO2 hydrogenation reactions, which is attributed to the tandem reactions of methanol synthesis on the Pd/SiO2 core catalyst and methanol dehydration to hydrocarbons on the H-ZSM-5 shell. The Pd/SiO2-SZ capsule catalyst has a similar mesoporous structure, narrow range of Pd particles size distribution, and consistent reduction characteristics to the Pd/SiO2 core catalyst. It maintains the physical and chemical properties of the core catalyst throughout the H-ZSM-5 shell synthesis process. Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy results reveal that the H-ZSM-5 zeolite shell completely encapsulates the Pd/SiO2 core catalyst. Compared with the crushed capsule catalyst (Pd/SiO2-SZP), the well-defined-structured Pd/SiO2-SZ catalyst has a much higher LPG selectivity of 33.6 %, owing to the well-matched reactions at the Pd/SiO2 core and H-ZSM-5 shell.