Catalytic Conversion of Mixed C_4 Hydrocarbons over ZSM-5/ZSM-57 Composite Zeolite Catalyst

The catalytic performance of a ZSM-5/ZSM-57 composite zeolite catalyst for the conversion of mixed C4 hydrocarbons was investigated. The acidic properties of the ZSM-5/ZSM-57 composite zeolite catalyst were characterized by means of ammonia temperature-programmed desorption (NH3-TPD) and pyridine adsorption Fourier transform infrared (FT-IR) spectroscopy. Results indicated that compared with ZSM-5 zeolite, the ZSM-5/ZSM-57 composite zeolite with lower ZSM-5 content showed higher catalytic activity and higher selectivity for ethylene and propylene because of its enhanced acidic strength and increased acid amount. ZSM-57 has small pores in the composite zeolite and this is beneficial in the shape-selective reaction of ethylene and propylene. On the contrary, the ZSM-5/ ZSM-57 composite zeolite with higher ZSM-5 content exhibited higher selectivity for benzene and toluene. This probably results from the pore structure and the structure matching property of the ZSM-5/ZSM-57 composite zeolite, which favors the aromatization of mixed C4 hydrocarbons.