Abstract: The modified ZSM-5 with different Zn loadings and the Zn, Mg and P composite modified ZSM-5 catalysts were prepared by ultrasonic impregnation method, the catalyst samples were characterized by XRD, N₂ adsorption-desorption, NH₃-TPD and Py-FTIR techniques, and the effects of different modification processes on the performance of direct synthesis of p-xylene from methanol were investigated in a fixed bed microreactor. The results show that the ZSM-5 zeolite modified by Zn can effectively improve the aromatization performance, providing a high reactivity level for direct production of p-xylene from methanol. At the optimum Zn loading, Mg and P were further introduced into the zeolite to modify the acidic properties and pore structure, covering the acidic site of the pore and narrowing the pore orifice, thus optimizing the catalytic selectivity for the formation of the target product p-xylene. The complex modified zeolite Zn-Mg-P/HZ-5 catalyst has a lifetime of 36 h, a para-selectivity of 96.00% and a p-xylene selectivity of 18.43%.

Key words: p-xylene, ZSM-5 zeolite, multiple modification, methanol