Effects of oxygen vacancy defect on microwave pyrolysis of biomass to produce high-quality syngas and bio-oil: Microwave absorption and in-situ catalytic

This paper proposed to use ferric oxide (Fe2O3) and ferroferric oxide (Fe3O4) as catalysts with both microwave absorption and catalytic properties. Carbon dioxide (CO2) was introduced as the reaction atmosphere to further improve the quality of biofuel produced by microwave pyrolysis of food waste (FW). The results showed the bio-gas yield and the syngas concentration (H-2 + CO) increased to 70.34 wt% and 61.50 mol%, respectively, using Fe3O4 as the catalyst. The content of aliphatic hydrocarbons in bio-oil produced with the catalyst Fe2O3 increased to 67.48% and the heating value reached 30.45 MJ/kg. Compared with Fe2O3 catalyst, Fe3O4 exhibited better microwave absorption properties and catalytic properties. Transmission electron microscopy (TEM) and Electron paramagnetic resonance (EPR) characterizations confirmed that the crystal surface of Fe3O4 formed more oxygen vacancy defects and unpaired electrons. Additionally, according to the X-ray photoelectron spectroscopy (XPS) analysis, the content of lattice oxygen in Fe3O4 was 14.11%, a value that was much lower than Fe2O3 (38.54%). The oxygen vacancy defects not only improved the efficient utilization of microwave energy but also provided the reactive sites for the reaction between the volatile organic compounds (VOCs) and CO2 to generate CO. This paper provides a new perspective for selecting catalysts that have both microwave absorption and catalytic properties during the microwave pyrolysis of biomass. (C) 2021 Elsevier Ltd. All rights reserved.