Zn/ZSM-5中Zn的赋存状态对其催化性能的影响

INFLUENCE OF STATUS OF Zn SPECIES IN Zn/ZSM-5 ON ITS CATALYTIC PERFORMANCE

利用原位水热合成法、液相离子交换法、等体积浸渍法、机械混合法以及固相离子交换法制备具有不同赋存状态的Zn改性ZSM-5分子筛(Zn ZSM-5),并通过X射线衍射、透射电镜、27 Al魔角旋转核磁共振谱等手段对Zn的赋存状态进行全面表征。结果表明:利用原位水热合成以及液相离子交换法可使Zn物种以Zn 2+形式迁移至分子筛阳离子位;机械混合法以及固相离子交换法可使Zn物种以骨架外ZnO的形式赋存于分子筛表面;等体积浸渍法引入的Zn物种同时以赋存于阳离子位的Zn 2+以及分子筛外表面的ZnO颗粒形式存在;Zn物种与分子筛之间的协同作用使得Zn ZSM-5分子筛在正庚烷催化裂解反应中提高了BTX(苯、甲苯、二甲苯)的收率及选择性。

Zn modified ZSM-5 zeolites with various Zn status were prepared by different methods(in situ hydrothermal synthesis,mechanical mixing,incipient wetness impregnation,solid-state ion exchange,and liquid phase ion exchange)and systematically investigated by X-ray diffraction(XRD),transmission electron microscope(TEM),27 Al magic-angle spinning(MAS)NMR techniques.The results proved that both the in-situ hydrothermal synthesis and the liquid phase ion exchange methods could facilitate the migration of zinc species into cation site of zeolites in the form of Zn 2+.The mechanical mixing and the solid-state ion exchange methods promoted the formation of extra-framework ZnO nanoparticles that were mainly located on the external surface of zeolites.While,the incipient wetness impregnation method promoted part of the Zn species into cation site of zeolites and part of the Zn species on the external surface of zeolites,simultaneously.The synergistic effect between Zn species and zeolites makes ZSM-5 zeolite modified by Zn have outstanding catalytic performance.