Catalytic fast pyrolysis of jujube sawdust over two core–shell micro/mesoporous zeolites: Impact of mesoporous structure and aluminum sources

Abstract

Core–shell zeolites have been used to improve bio-oil quality in biomass catalytic fast pyrolysis (CFP), yet research on shell materials remains limited. This study explores ZSM-5@MCM-41 and ZSM-5@SBA-15 core–shell micro/mesoporous zeolites, including their Al-containing variants synthesized with sodium aluminate (SA), aluminum sulfate (AS), and aluminum isopropoxide (AI) as Al sources, for improving bio-oil quality during biomass CFP. The samples were thoroughly characterized using powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N₂ adsorption–desorption, and NH₃-TPD techniques. CFP experiments using jujube sawdust examined the impact of mesoporous structure and Al sources on bio-oil yield and quality. Results indicated that ZSM-5@MCM-41, with a smaller mesoporous structure and higher acid strength, showed 1.7 times greater hydrocarbon selectivity compared to ZSM-5@SBA-15 (20.6 % vs. 12.4 % by area). The incorporation of Al into the MCM-41 shell led to a decrease in bio-oil yield, with the order being ZSM-5@MCM-41 > ZSM-5@MCM-41-AI > ZSM-5@MCM-41-AS > ZSM-5@MCM-41-SA, owing to the combined effects of strong acid sites and mesoporosity. However, the hydrocarbon selectivity of ZSM-5@Al-MCM-41 catalysts decreased by 15.6–19.5 % owing to reduced mesoporous volume. Conversely, while the incorporation of Al in the SBA-15 shell also reduced bio-oil yield, it increased hydrocarbon production by 27.0–47.6 %. Also, the hydrocarbons selectivity was related to the acid strength of the ZSM-5@Al-SBA-15 catalysts, demonstrating that strong acid sites are more effective in regulating bio-oil quality than porosity.