Influence of zeolite confinement effect on its acidic characterization and catalytic performance
As an important carrier of acid-catalyzed thermal reaction,zeolite has the advantages of controllable acidity,strong thermal stability and shape selectivity,but its special rigid pore structure and internal charge distribution make it have a limiting effect,which will affect the zeolite's acidic characterization and catalytic reaction performance.Since the catalytic role of zeolite is mainly the Brønsted acid site,the formation mechanism of the Brønsted acid site and the confinement effect is introduced,the influence of the restriction effect on the acid strength and acid density characterization of the Brønsted acid site is briefly described,and the influence of spatial constraint and local electric field on the catalytic reaction performance in the restriction effect is reviewed.It is pointed out that in the acidic characterization,spatial constraints limit the accessibility of probe molecules to acid sites,which further affects the measurement of acid density.The local electric field affects the adsorption and desorption of probe molecules,which in turn directly affects the acid intensity.Therefore,in the acidic characterization of zeolites,probe molecules with similar size and structure to reactants should be selected to measure the acid density and acid strength that can be acquired as the actual results close to the Brønsted acid site.In catalytically dominated thermochemical reactions,spatial constraints make zeolites shape-selective,and the reaction process,intermediate-transition-state product and final product distribution of thermochemical reactions can be selected by controlling the pore size of zeolite.At the same time,since the local electric field affects the apparent acid intensity,the catalytic performance of zeolite is related to the apparent acid intensity.The smaller the pore size of the zeolite,the greater the van der Waals interaction of the reaction molecules,which affects the formation of the transition state of the reaction and then changes the activation energy of the reaction,thereby affecting the catalytic thermochemical reaction efficacy.Comprehensive analysis shows that only a zeolite with appropriate acid strength and an accessible pore size similar to that of the reactant molecule is an ideal acid carrier for catalyzing the thermal reaction.