Synergistic oxidation-reforming of biomass for high quality syngas production based on a bifunctional catalyst

Conventional O₂ gasification for low-rank biomass/sludge conversion is prone to high CO₂ concentrations in the syngas because of its high O content and low calorific value. This study establishes a synergistic oxidation-reforming reaction route for the conversion of low-rank carbon-containing resources into high-quality syngas. The efficient oxidation-reforming reaction is based on the bifunctional catalyst NiO–Fe₂O₃/Al₂O₃, which includes Fe₂O₃ oxidation sites and NiO reforming sites. Hydrogen temperature-programmed reduction, together with X-ray diffraction and X-ray photoelectron spectroscopy experiments, demonstrated that the two functional active sites have strong interactions with the support, leading to efficient cooperation between the oxidation reaction and reforming reaction with regards to both the reaction sequence and C/H/O element balance. Syngas produced from biomass/sludge based on oxidation-reforming reactions has an extremely low CO₂ concentration of approximately 3%, and the valid gas (CO, H₂) concentration exceeds 95%. The valid gas yield of walnut shell reached 1452.9 mL/g, the total gas yield was 1507.2 mL/g, and the H₂/CO ratio was 1.02, which are all very close to the theoretical maximum values of 1553.1 mL/g and 1.01, respectively, demonstrating that the inherent CO₂/H₂O along with CH₄/tar species were efficiently converted to H₂ and CO through oxidation-reforming reactions. During a 60-cycle test, NiO-Fe₂O₃/Al₂O₃ exhibited good redox stability.