Hydrogen-rich syngas production with tar elimination via biomass chemical looping gasification (BCLG) using BaFe2O4/Al2O3 as oxygen carrier

•A modified direct decomposition method was applied for the preparation of 30ABF.•30ABF was found to be excellent for biomass gasification.•Ferrite can be fully reduced to Fe0 and exhibits a good regeneration property.•The forming of CO* is the main rate determining step revealed by DFT analysis. Biomass chemical looping gasification (BCLG) is a promising technology for biomass utilization. The selection of appropriate oxygen carrier (OC) is one of the key issues in BCLG process. In this work, 30% Al2O3/BaFe2O4 (30ABF) synthesized via the direct decomposition method coupled with mixed calcination process was applied as OC in BCLG for hydrogen-rich syngas production. 30% Al2O3/Fe2O3 (30AF) was prepared by incipient wet impregnation method for comparison. Gasification experiments were conducted in a fixed bed reactor. The effects of OC-biomass mixing method, ratio of OC and biomass (O/B), temperature and steam feeding rate on the performance of BCLG were investigated. The results indicated that 30ABF exhibited a high reactivity with char but a low reactivity with syngas. The hydrogen-enriched syngas was obtained when O/B was 0.6 and steam volume fraction of 33.6% at 850 °C. The properties of the fresh and used OCs were characterized using different methods including XRD, SEM, BET and XPS. To deeply understand the reaction mechanism, adsorption of C atom over BaFe2O4 surface was analyzed by the method of density function theory (DFT). It was found that the energy barriers of CO* forming and dissociation were 0.252 eV and 0.165 eV, respectively. Thus the forming of CO* is the main rate determining step. The thermodynamic calculation results indicates that ΔG(T, p) of total system at 900 °C was −2.621 eV.