Rice husk-derived sheet-like ZSM-5 zeolites with preferred c-axis orientation: Synthesis and catalytic performance in biomass fast pyrolysis

The sustainable valorization of agricultural waste into high-performance catalytic materials represents a critical pathway toward the circular economy and renewable energy production. Herein, we report a one-pot hydrothermal synthesis of c-axis-oriented sheet-like ZSM-5 zeolites (S-ZSM-5) using silicalite-1 seeds and rice husk (RH)-derived amorphous silica as a renewable and environmentally benign sole silicon source, without expensive organic structure-directing agents or additional growth-directing additives. The slow dissolution of solid amorphous silica, in synergy with seed-induced nucleation, created an anisotropic growth environment consistent with the competitive growth model, directing preferential crystal growth along the c-axis and led to intergrown S-ZSM-5 nanosheets with intercrystalline mesopores. The seed-to-silica molar ratio served as a key parameter for tuning the hierarchical pore structure of the resulting S-ZSM-5 zeolites. The optimized S-ZSM-5-0.2 catalyst exhibited a high BET surface area of 346 m2·g−1, a mesopore volume of 0.09 cm3·g−1, and abundant strong acid sites. In the catalytic fast pyrolysis (CFP) of corn stalk, S-ZSM-5-0.2 achieved a maximum benzene, toluene, and xylene (BTX) yield of 91.68 mg·g−1, representing a 21% enhancement over conventional ZSM-5 synthesized from TEOS (75.84 mg·g−1). The c-axis-oriented short straight channels of this material significantly enhanced molecular diffusion and mass transfer, promoting deoxygenation and aromatization reactions while effectively suppressing coke formation (as confirmed by a reduction in coke deposition from 13.15 wt% to 10.81 wt%). This work provides a straightforward and scalable strategy for economical converting agricultural waste into hierarchical zeolites with a tailored crystal orientation, offering a promising and sustainable route for biomass-to-aromatics conversion and advancing the development of waste-derived catalysts for green chemistry applications.