Upcycling Rice Husk for Hierarchical ZSM-5 Zeolite Synthesis in Glycerol-To-Acrolein Conversion

This research explores a novel dual-functional strategy for synthesizing hierarchical ZSM-5 zeolites using rice husk ash (RHA), a rice milling byproduct rich in silica and hydrocarbons, which simultaneously acts as both silicon source and carbonaceous template. RHA serves as both a green silica source and a natural carbon template, enhancing the zeolites’ thermal stability, acid strength, and porosity for molecular diffusion. The RHA-derived ZSM-5 catalysts exhibited exceptional efficiency in glycerol dehydration, attaining glycerol conversion rates as high as 83% while maintaining an acrolein selectivity of 99.8%. Solid-state nuclear magnetic resonance spectroscopy (ssNMR) investigations revealed that these catalysts possess a high density of total acid sites (up to 1.04 mmol/g) and a hierarchical pore structure, both of which are crucial for improved catalytic activity and reduced coke formation. Furthermore, the study provides insights into the reaction mechanisms of glycerol dehydration and coke formation, highlighting the role of hierarchical porosity in enhancing the diffusion of reactants and products, thus prolonging catalyst life. This approach not only provides a sustainable alternative for catalyst production by upcycling agricultural waste but also establishes a new structure–function relationship between hierarchical porosity and coke resistance, thereby offering both scientific insight and practical value for green catalysis.