Electronic–Oxygen Synergy at Ca-Fe Dual-Metal Interfaces for Selective Syngas Regulation in Biomass Chemical Looping Gasification

This study reveals the efficient catalytic role of Ca-Fe-based oxygen carriers (Ca₂Fe₂O₅) in biomass chemical looping gasification. With oxygen carrier introduction, the CO yield doubled (0.13 Nm³/kg→0.26 Nm³/kg), with 76.10% selectivity. Steam co-feeding further increased the H₂ yield from 0.19 Nm³/kg to 0.72 Nm³/kg, significantly elevating the H₂/CO ratio to 2.62. Combined with density functional theory (DFT), the micro-mechanism of reduced oxygen carrier surfaces activating CO₂/H₂O was elucidated. CO₂ (adsorption charge -0.952 |e|) and H₂O (adsorption charge -0.612 |e|) chemically adsorb at the CaO(111)/Fe(110) interface, where Fe atoms (charges 0.433 |e|, 0.927 |e|) act as electron donors to drive efficient molecule activation. CO₂ undergoes single-step splitting (CO₂→CO* + O*), with the desorption energy barrier (<i>E</i>_a = 1.09 eV, 105.17 kJ/mol) determining the reaction rate. H₂O splits via two-step cleavage (H₂O→HO* + H*→2H* + O*), which is rate-limited by the first step (<i>E</i>_a = 0.42 eV, 40.52 kJ/mol). Simultaneously, the reduced oxygen carrier achieves oxidative regeneration through surface O* lattice incorporation. This work atomically reveals the "electron transfer-oxygen transport" synergy at the Ca-Fe bimetallic interface, establishing a theoretical framework for the directional regulation of the syngas composition and the design of high-performance oxygen carriers.