Reaction mechanism of methane conversion over Ca2Fe2O5 oxygen carrier in chemical looping hydrogen production

Density functional theory (DFT) calculations were employed to explore the reaction mechanism of methane conversion over Ca2Fe2O5 oxygen carrier in chemical looping hydrogen production. The elementary reaction steps, including CH4 activation, CO and CO2 formation, H2 and H2O generation, and oxygen diffusion, were investigated to propose the reaction network. It was found that the H2 generation is very difficult on the surface of Ca2Fe2O5 oxygen carrier and the H atoms tend to react with surface oxygen to form H2O molecule. The CO formation is prone to occur and the generated CO molecule is very easily oxidized by surface oxygen to form the CO2 molecule. The surface oxygen of Ca2Fe2O5 oxygen carrier could exhibit the excellent reactivity. The oxygen diffusion needs to overcome a high energy barrier and it is an inherent high-temperature process. For the whole reaction of methane conversion over Ca2Fe2O5 oxygen carrier, the CH4 activation process is the dominant rate-determining step. In order to increase the CH4 reactivity of Ca2Fe2O5 oxygen carrier, it is necessary to find promoters that could decrease the energy barrier of CH4 activation and enhance the oxygen diffusion ability.