关键词: 镓, ZSM-5, 锌, 甲醇, 芳烃

Abstract: GaZSM-5 zeolite was prepared by hydrothermal synthesis method followed by acid exchange and pelletization. A series of zinc modified GaZSM-5 zeolites was prepared by wet impregnation, mechanical mixing and ion exchange, denoted by WI, PM and IE, respectively. The catalysts were characterized by XRD, SEM, FT-IR, XPS, ICP, low temperature N2 physical adsorption and desorption, NH3-TPD and Py-IR. The catalytic performance in the reaction of methanol to aromatics was evaluated in a fixed bed reactor. The results indicated that preparation method had no effect on the crystal structure but regulated the pore distribution. The zinc modification decreased the strong acid amount, weakened strong acid and enhanced the ratio of L acid to B acid. There were two kinds of zinc species, i. e. ZnO species on the crystal surface and non-framework Zn species with strong interaction with the framework, both of the two zinc species could increase the aromatic selectivity. The catalyst with zinc mass content exceeding 3.0% made by wet impregnation would deactivate quickly. The catalyst made of mechanical mixing method had the average aromatics selectivity of 44.39% at 216 h operation due to the best effective synergetic of B acid sites and zinc active sites.

Key words: Ga, ZSM-5, zinc, methanol, aromatics