The effect of ZSM-5 catalyst support in catalytic pyrolysis of biomass and compounds abundant in pyrolysis bio-oils

• Biomass catalytic pyrolysis over bulk/supported ZSM-5 and Al2O3 support compared.
• Brønsted acidity enhances liquid selectivity in biomass catalytic pyrolysis.
• Catalytic Lewis sites promote alkylation and cyclization.
• The Al2O3 catalyst support promotes coke formation and reduces aromatics.

Supported ZSM-5 is commonly used for in-situ biomass pyrolysis vapor upgrading in fluidized bed reactors. In this work, we investigate the effects of catalyst support on the pyrolysis product distribution by studying pyrolysis of woody biomass and bio-oil derived model compounds. Specifically, miscanthus, toluene and furan are catalytically pyrolyzed over bulk ZSM-5, supported ZSM-5 and a commercial Al2O3 support. The pyrolysis product distributions of biomass and each model compound are presented and discussed. The coke formed on the catalysts and support, which is also responsible for catalyst deactivation, is analyzed using temperature programmed oxidation (TPO). It is shown that pyrolysis of miscanthus, toluene and furan over supported ZSM-5 produces less liquid products, particularly mono-aromatic hydrocarbons, than over bulk ZSM-5, mainly due to the dilution of Brønsted acid sites by the catalyst support. The Lewis acidity of the Al2O3 support promotes alkylation and cyclization of propylene leading to enhanced benzene production. The Lewis acidity of the support also enhances coke production with a less condensed structure, while selectivity to poly-aromatics is deteriorated.