原位DRIFTS研究分子筛Bronsted酸和Lewis酸催化戊烯转化的作用机理

Mechanisms of Bronsted and Lewis acids of zeolite on pentenes conversion by in situ DRIFTS

本研究基于原位水热合成和气相浸渍的方法分别合成了含有Bronsted/Lewis酸的Beta分子筛和只含有Lewis酸的AlCl_(3)@Si-Beta样品,并通过原位漫反射红外技术对比研究了Bronsted酸和Lewis酸催化直链和侧链戊烯同分异构体转化作用机理的差异。结果表明,同时含有Bronsted/Lewis酸的Beta分子筛中,Bronsted酸起主要的活化作用,催化戊烯进行异构和叠合反应时均遵循经典的碳正离子机理;而AlCl3@Si-Beta中的Lewis酸不含氢质子或羟基,催化α-戊烯进行双键迁移和2-戊烯的顺反异构反应时遵循AB-AD机理,以类烯丙基物种作为中间体,无法催化戊烯进行骨架异构和叠合反应。

Zeolites have been extensively used in the chemical and petrochemical industries owing to their tunable acidities and unique pore structures.Beta zeolite with Bronsted and Lewis acids and AlCl_(3)@Si-Beta with only Lewis acid were prepared by hydrothermal synthesis and gas-phase impregnation methods,respectively.Mechanisms differences of Bronsted and Lewis acids on four pentene isomers transformation were investigated by in situ diffraction infrared Fourier transform spectrum(DRIFTS).The results suggested that Bronsted in Beta played a main role in isomerization and oligomerization reactions which all followed classical carbenium ion mechanisms.On the contrary,Lewis acid in AlCl_(3)@Si-Beta without hydrogen proton or hydroxyl catalyzed α-pentene doublebond migration to produce β-pentene and cis-trans isomerization reaction of 2-pentene by AB-AD mechanism with allyl-like species as intermediates,and could not catalyze pentenes skeletal isomerization and oligomerization reactions.