Product Modification in Catalytic Fast Pyrolysis of Corn Stalk: The Decoupled Effect of Acidity and Porosity within a Core-Shell Micro-/ Mesoporous Zeolite

The large production of biomass waste is causing worldwide concern about its low-value application and toxic potential. Catalytic fast pyrolysis (CFP) is a promising method to convert biomass wastes into value-added transportable fuels. However, this route is limited by the production of highly oxygenated bio-oil. Zeolites are effective in removing oxygen, and the resulting product is strongly dependent on the porosity and acidity of the zeolites. Currently, studies on the role of zeolite parameters on the deoxygenation of bio-oil are lacking, owing to the interplay between mesopore diffusion and acidity. Herein, we decoupled the role of these parameters by selecting the core-shell micro-/mesoporous zeolite ZSM-5@SBA-15 as the catalyst model and studied their effect on the pyrolysis pathway of corn stalk. A series of ZSM-SgSBA-15 catalysts were synthesized with varied shell thicknesses, shell acidity, and core acidity. In the CFP of corn stalk, it was demonstrated that the mesopores in the SBA-15 shell facilitated the mass transfer of biomass pyrolysis vapors, while the acidity of the ZSM-5 inner core promoted their catalytic transformation to aromatic hydrocarbons. In contrast, the acidity of the SBA-15 shell exhibited an adverse effect by inducing the repolymerization of oxygenated intermediates to form coke. Among all the tested catalysts, the ZSM-5(15)@SBA-15-1 catalyst with an internal silicon-to-aluminum ratio of 15 and a mesopore diffusion length of similar to 75 nm exhibited the highest production of hydrocarbons and phenols.