Insights into reactive behaviors and mechanisms of nickel-based oxygen carriers doped by Fe/Co during chemical looping combustion from multiple-scale molecular modeling combined with experiments

Understanding reactive behaviors and mechanisms of oxygen carriers (OCs) is a key issue in chemical looping combustion (CLC), which can provide ideas and routes not only for constructing high-performance OCs, but also for designing reactors and systems intensification. However, various points about the reaction behaviors and oxygen release mechanism of iron/cobalt-doped nickel-based OCs in CLC remain unclear and highly desired to elucidate. Therefore, this work determines reactive behaviors and mechanisms of Fe/Co-doped nickel-based OCs using multiple-scale molecular modeling and experiments. The interaction between molecules and OCs surfaces was characterized using independent gradient modulus to directly visualize interaction region, type, and intensity; they were further quantified through energy decomposition analysis. The reaction path and coordinates in elementary reactions were explored based on DFT calculations, and the structures, energies, and electronic properties were obtained. According to calculated reaction energy barriers, Fe doping enhanced activity of nickel-based OCs, whereas Co doping reduced. Furthermore, nickel-based OCs were prepared and tested using thermo-gravimetric analysis (TGA) and temperature-programmed H2 reduction. Despite slight numerical differences, TGA-based apparent activation energies agreed well with DFT predications. Additionally, the effects of chemical bonding, surface structure, particle size and defects of OCs on the intrinsic and non-intrinsic reactive properties were revealed based on material characterizations.