Progress in the synthesis of hierarchical zeolites for diffusion intensification
Traditional microporous zeolites have uniform pore size,large specific surface area,strong acidity,ion exchange ability,and good shape selectivity.However,the traditional microporous zeolites suffer from high mass transfer and diffusion resistance,seriously reducing their performance.Hierarchical zeolites possess a multi-level pore structure,which can enhance the diffusion of large molecules,reduce coke accumulation,and improve catalysts'utilization,lifespan,and catalytic performance.Hierarchical zeolites are usually prepared by either"top-down"method or"bottom-up"strategy.This article mainly reviews the synthesis methods of hierarchical zeolites in recent years,and focuses on the"top-down"method with wide applications.The research on diffusion intensification for hierarchical zeolites in catalytic applications is comprehensively reviewed.It is pointed out that hierarchical zeolites have unique advantages in improving catalytic performance(such as activity,selectivity,catalytic stability).By introducing hierarchical pores in the framework of zeolites,the diffusion path within the zeolitic crystal is shortened,and the mass transfer diffusion restrictions are reduced.Hierarchical pore structure is also conducive to stabilize loaded metal active species,inhibiting their sintering in catalytic reactions and increasing the stability of supported zeolite catalysts.Finally,the advantage of hierarchical zeolites are discussed,i.e.strengthening internal diffusion performance and improving the utilization rate of internal centers in zeolites,and their preparation method and green production process are prospected.
hierarchical zeolitemass transfer limitationdiffusion intensificationcatalysis
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