Density functional theory study on the reaction between hematite and methane during chemical looping process

We present a first principles study using periodic density functional theory on the reaction between α-Fe2O3 and CH4 during chemical looping process. The sequential processes of methane dissociation, hydrogen formation, water production and dissociation, and carbon selective oxidation on α-Fe2O3 (001) surface were explored. It was found that the sequential dissociations of CH4 were the dominant rate-determining process. Although H2 production was less favorable than H2O production, the formed H2O can be dissociated facilely to increase the surface H concentration at chemical looping conditions. CO production is more favorable than CO2 production, while CO2 can also be produced in the high-temperature process. Subsequently, the oxygen migration in α-Fe2O3 (001) surface was also investigated, indicating the O migration from inner bulk to surface layer is inherently a high-temperature process. Our results are consistent with the kinetic experiments. In order to improve the CO selectivity in CH4 chemical looping process for syngas production, we need to find promoters which could decrease the activation barrier of CH4 sequential dissociation steps and increase the oxygen migration ability of oxygen-carriers.