Recent advances in biomass-assisted synthesis of hierarchical porous zeolite

Abstract

Zeolites have long been considered the most important catalysts in petrochemical refineries due to their large surface areas, exceptional chemical and thermal stability and abundant active sites, but their microporous features also cause mass-transfer limitation and inaccessibility of active sites for large molecules. To overcome the transport constraints and improve the catalytic activity, a number of strategies have emerged, most of which employ expensive templates or complex post-processing, usually causing environmental or economic issues. In this review, we attempt to organize and overview the effect and mechanism of the preparation of hierarchical zeolites by green and cheap bio-templates combined with various strategies on their pore structure and acidity, involving hydrothermal synthesis, steam-assisted crystallization, etc. This will facilitate the synthesis of hierarchical zeolites with high transport efficiency and tuning acidity, further improving their performance in catalysis, adsorption, etc. Some summary tables are provided to enable the readers to compare the corresponding intergranular or intragranular mesoporous characteristics and rules of the obtained hierarchical zeolites. If more in-depth research can be carried out to solve the current challenges, biomass-assisted synthesis of hierarchical zeolite will become an economic and green industrial route.