One-step preparation of toluene/xylene from benzene and syngas over ZnAlCrOx&HZSM-5 bifunctional catalyst

Compared with the traditional alkylation reaction of methanol and benzene, the one-step process of syngas and benzene to toluene/xylene has the advantages of high benzene conversion, good catalyst stability, and high economic efficiency. In this study, a series of Zn-based metal oxides were coupled with H-ZSM-5 zeolite to form bifunctional catalysts for the efficient conversion of syngas and benzene into toluene and xylene, and the optimal bifunctional catalyst was ZnAlCrOx &H-ZSM-5. In-situ FT-IR analysis showed that the conversion of syngas alone on the catalyst was weak, but after the addition of benzene, the alkylation reaction of benzene with methoxy species can effectively prompt the conversion of syngas, indicating the synergy between the metal components and zeolite components in bifunctional catalyst. The modifying of H-ZSM-5 zeolite with Zn, Mg, Ga elements to reduce the ratio of B acid to L acid in zeolite was found to contribute to the conversion of benzene. Among them, the ratio of B acid to L acid was the lowest after Zn modification, and the conversion of benzene was also the highest. The degree of benzene alkylation can be controlled by adjusting the reaction temperature, the space velocity of raw materials, and the H2/CO ratio of in syngas, and the product selectivity can be adjusted. Under the reaction conditions of pressure 3MPa and temperature 400℃, ZnAlCrOx&H-ZSM-5 bifunctional catalyst gives both high benzene conversion (90.6%) and toluene/xylene selectivity (74.3%), and the effective utilization rate of CO is 33.7%. © 2022 Chemical Industry Press. All rights reserved.