Catalytic upgrading of biomass pyrolysis volatiles over Y zeolites modified with different metal oxides

Pyrolysis as one of the most utilizations of biomass has aroused the increasing attention, however, the key is to upgrade biomass pyrolysis volatiles and enrich the high-valued chemicals in bio-oil. In this paper, different metal oxide-modified Y zeolites, including Fe/Y, Co/Y, Ni/Y, Mg/Y and Zn/Y, were prepared by wet impregnation and employed in catalytic upgrading of pyrolytic volatiles from rice straw (RS) and poplar sawdust (PS). Results showed that the modification by metal oxides led to the decrease of surface area and the changes in the acidity of zeolites. Higher yields of gas and water were obtained over metal oxide-modified zeolites at the expense of the bio-oil yields. More strong acid sites of the Ni/Y and Zn/Y catalysts promoted the generation of H2. Fe/Y catalyst showed good selectivity to aromatics in bio-oil owing to high mesoporous volume and strong deoxidization capacity. The highest aromatic hydrocarbons content (63.0%) was obtained over Fe/Y in RS bio-oil. The formation of phenol and cresol was promoted with increasing the ratio of Lewis/Bro<spacing diaeresis>nsted acid. Under the action of Ni/Y with the highest Lewis/Bro<spacing diaeresis>nsted ratio, the phenol content in bio-oil from RS and PS pyrolysis was enhanced to 11.8% and 25.3%, respectively. The Fe/Y catalyst had good upgrading performance during three reactionregeneration cycles. In addition, the possible reaction mechanism of biomass pyrolysis volatiles over metal oxide-modified Y zeolites was proposed. This work will provide a guide for the composition regulation of bio-oil from biomass pyrolysis.