锌改性HGaZSM-5分子筛催化甲醇制芳烃(MTA)反应性能

Zn MODIFICATION OF HGaZSM-5 AND ITS CATALYTIC PEFORMANCE IN METHANOL TO AROMATICS REACTION

通过水热合成法制得GaZSM-5分子筛,经酸交换得到氢型分子筛HGaZSM-5。采用浸渍法、机械混合法和离子交换法制备出一系列Zn改性GaZSM-5分子筛,分别记作WI,PM,IE。采用XRD、SEM、FT-IR、XPS、ICP、低温氮气吸附-脱附、NH 3-TPD和Py-IR等技术对其进行物化性质表征,并在连续流动固定床反应器上进行甲醇制芳烃(MTA)反应性能评价。结果表明,改性方法对分子筛的晶体结构没有影响,对孔径分布数量有一定的调变作用。锌改性降低了强酸强度并减少强酸量,提高L酸比例。氧化锌和与骨架有强相互作用的锌均能提高芳烃选择性,浸渍改性的锌负载量(w)超过3.0%时会导致催化剂快速积炭失活。机械混合法所得分子筛的B酸和锌活性中心的协同作用最好,平均芳烃选择性达到44.39%,使用寿命为216 h。

GaZSM-5 zeolite sieve was prepared by hydrothermal synthesis method followed by acid exchange and pelletization.A series of Zn 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,NH 3-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 Zn modification decreased the strong acid amount,weakened strong acid and enhanced the ratio of L acid to B acid.There were two kinds of Zn species,i.e.ZnO species on the crystal surface and non-framework Zn species with strong interaction with the framework,both of the two Zn species could increase the aromatic selectivity.The catalyst with Zn mass fraction 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 Zn active sites.