Adsorption or deoxidation of H2 interacted with Fe3O4 surface under different H coverage: A DFT study

The adsorption and dissociation of H2, the migration ability of H atom, as well as the competition relationship between adsorption or deoxidation of H2 with increasing of H adsorption coverage on the Fe3O4 (1 1 1)-Fetet1 and (0 0 1)-B surfaces were systematically studied by DFT + U method. The adsorption energy and the optimal dissociation barrier of H2 on two Fe3O4 surface is about 0.04 eV and 1.0 eV, respectively. The surface O site is the most favorable adsorption site for H and the dissociated H2 is adsorbed on the adjacent surface O atoms. When H coverage is low, H preferentially adsorbs to the most stable O sites with the maximum adsorption heat. With the increasing of H coverage, the adsorption heat gradually decreases. When H coverage approaches saturated coverage, H2 reacted with surface O to form H2O become more favorable than direct adsorption. The phase diagrams of H adsorption/deoxidation at different temperature and pressure ranges were calculated. It can be found that the reduction of surface O become more favorable with the increasing of H coverage. The results indicate that the degree of reduction difficulty of surface O can be controlled by changing the coverage of H by adjusting the reaction condition.