Improvement of H₂-rich gas production with tar abatement from pine wood conversion over bi-functional Ca₂Fe₂O₅ catalyst: Investigation of inner-looping redox reaction and promoting mechanisms

The objective of this research was to find cost-effective inner-looping redox-reaction-based biomass conversion catalysts by screening five Fe-containing materials through the integration of pine wood pyrolysis and gasification. All the evaluation tests are conducted in a fixed bed reactor under atmospheric pressure. The effect of temperature, water injection rate (steam/biomass ratio), catalyst loading, and reaction time on pine wood conversion performances was investigated. Ca₂Fe₂O₅ catalyst was found to facilitate H₂-rich gas production, tar abatement, and carbon conversion. The maximum H₂ yield of 7.12 mol·H₂/kg·Biomass was obtained in the first 10 min of gasification, which increased H₂ yield by 78.98% compared to biomass gasification under the water injection rate of 0.10 mL/min and catalyst load amount of 10 wt.% at 850 °C. Moreover, the hydrogen utilization, carbon conversion, and total gas yield of the process due to the use of Ca₂Fe₂O₅ increase by 13.4%, 17.3%, and 11.7%, respectively. Continuous high yields of H₂-enriched syngas were observed during the cyclic stability tests, indicating significant activity and redox durability of Ca₂Fe₂O₅. The catalyst characterization using BET, XRD, H₂-TPR, SEM/EDS, and TEM revealed that Ca₂Fe₂O₅ is stable when tested cyclically, which results from the existence of Ca²⁺ in Ca₂Fe₂O₅. The bi-functional Ca₂Fe₂O₅ catalyst provides a novel way of inner-looping redox reaction for the continuous conversion of biomass.