Zeolite microspheres with hierarchical structures: formation, mechanism and catalytic performance

Abstract

An improved polymerization-induced colloid aggregation (im-PICA) method was developed to prepare zeolite microspheres (ZMSs) with a hierarchical porous structure and a uniform size, which could easily be carried out within half an hour by simply adding urea and formaldehyde into an acidic pH-pre-controlled colloidal solution as-obtained from a hydrothermal crystallization process. This procedure successfully avoided the repeated ultrasonic washing and high-speed centrifugation of the nanozeolite colloid during the traditional PICA method, and thereby became energy and time-economical. After removing the polymeric component, solid and hollow ZMSs as well as the mono-dispersed nanozeolite can be obtained under different preparation conditions. The structural transformation could be attributed to the correlation of the polymerization velocity on the zeolite nanocrystal surface and in the bulk solution with variation of acidity. Due to the short diffusion routes and abundant exposed active sites of nanozeolites as well as their unique secondary mesopore architecture, ZMSs displayed a clear advantage on catalysis reactions compared to commercial zeolite catalysts, such as the dehydration of fructose into 5-hydromethyl furfural.