改性ZSM-5分子筛高选择性催化甲醇制对二甲苯

采用超声浸渍的方法制备了不同Zn负载量的改性ZSM-5分子筛以及Zn、Mg和P复合改性ZSM-5分子筛，通过X射线衍射、N₂吸附-脱附、氨吸附-程序升温脱附和吡啶吸附-傅里叶变换红外光谱等手段对催化剂进行表征，并在固定床微型反应器上系统探究了不同改性过程对其催化甲醇直接制对二甲苯反应性能的影响。结果表明：Zn改性有效提高了ZSM-5分子筛的芳构化性能，可为甲醇制对二甲苯提供较高的催化活性基础；在最佳Zn负载量时，进一步引入Mg和P对分子筛酸性和孔道结构进行修饰，覆盖孔道酸性位以及窄化孔口，优化了催化剂择形性，有利于目的产物对二甲苯的生成。复合改性分子筛Zn-Mg-P/HZ-5催化剂寿命为36 h，对位选择性为96.00%，对二甲苯选择性（对二甲苯占总二甲苯的比例）高达18.43%，表现出优异的反应性能。

HIGHLY SELECTIVE CATALYTIC PERFORMANCE OF MODIFIED ZSM-5 ZEOLITE FOR PRODUCINGp-XYLENE FROM METHANOL

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%.