两段变温法水热合成多级孔ZSM-5分子筛及其催化裂化性能

摘要

以四丙基氢氧化铵(TPAOH)为单一模板剂,采用低温老化、高温晶化2段变温法合成出了球状多级孔 ZSM-5分子筛.利用XRD 、FT-IR、NH3-TPD、SEM、TEM以及氮气吸-脱附等测试对合成样品进行了表征.结果表明:直径约为2μm左有的球状多级孔ZSM-5分子筛颗粒内的晶间介孔和大孔主要由棒状纳米品堆积而成的,该产品具有较大的比表面积和介孔孔容.同常规水热法一步合成的微孔ZSM-5分子筛相比,2段变温法合成的多级孔ZSM-5分子筛具有更高的B酸/L酸比例(CBP/CLP)、强酸/弱酸比例(Cs/Cw)以及活性位可接近性指数(ACI).催化裂化评价结果显示,得益于活性位可接近性指数等指标的提高,球状多级孔ZSM-5分子筛比常规合成的微孔ZSM-5分子筛具有更高的转化率和丙烯收率等优异的催化性能.%Hierarchical ZSM-5 zeolites with regular spherical structure were successfully synthesized via a facile two stage varying temperature crystallization using tetrapropylammonium hydroxide (TPAOH) as the single template.The fabricated samples were characterized by means of XRD,FT-IR,NH3-TPD,SEM,TEM and N2 adsorptiondesorption isotherms.The results indicate that the spherical ZSM-5 zeolite particles with around 2 μm in diameter possess intercrystalline meso-and macropores generated from the aggregation of bar-shape ZSM-5 nanocrystals,which exhibit large specific surface area and mesopore volume.Compared to the ZSM-5 zeolite synthesized by constant temperature hydrothermal method,the hierarchical ZSM-5 zeolites have higher Br(o)nsted acid to Lewis acid ratio (CBP/CLP) and strong acid to weak acid ratio (Cs/Cw),as well as the enhanced accessibility of the active sites,which were very important to the catalytic reaction.Catalytic tests reveal that hierarchical ZSM-5-contained catalytic cracking catalyst exhibit an outstanding performance in improving the propylene yield and conversion due to the enhancement of accessibility.