Hydrogen-rich gas production from medicinal residue via chemical looping gasification over metal-modified iron oxygen carriers

Medicinal residue (MR) is an abundant but underutilized lignocellulosic waste, and efficient routes for converting it into hydrogen-rich gas remain limited by oxygen carrier (OC) design. Metal modification of iron oxygen carriers provides a practical strategy for tuning hydrogen-oriented biomass chemical looping gasification (BCLG) under steam. Fe, NiFe, KFe, and CuFe OCs were synthesized by a sol-gel route and evaluated under identical conditions in a two-stage fixed-bed reactor. Among the tested formulations, NiFe with a precursor ratio of 2:1 delivered the best overall performance, giving a H₂ yield of 37.40 mmol⋅g⁻¹, carbon conversion of 74.13%, and energy efficiency of 96.59%. Structural and redox characterization indicates that this behavior arises from the combined effects of higher surface accessibility, ferrite-type Ni-Fe interaction, and more favorable reducibility. These results identify Ni-modified Fe OCs as promising materials for biomass-to-hydrogen conversion.