First principle study on the interactions of NH3, NOx and O2 with Fe3O4 (1 1 1) surfaces

The interactions of NH3, NOx and O2 with two Fe3O4 (1 1 1) surfaces named Fetet- and Feoct-tet-terminated, respectively, were investigated by first principle calculation. The results indicated that the Feoct-tet-terminated surface had a stronger effect on the adsorption and activation of these small molecules overall. Specifically, NH3, NO and O2 tend to be stably adsorbed on the octahedral Fe site on the Feoct-tet-terminated surface. The energy released by O2 adsorption is the most among them, and it is easy to form abundant surface adsorbed oxygen on the catalyst surface, which further co-adsorb or combine with NO to form nitrate and nitrite species with various coordination structures. The chelated and bridged bidentate-coordinated nitrate species with the highest adsorption energies are important reaction intermediates in NH3 selective catalytic reduction (NH3-SCR). In addition, due to the horizontal adsorption configuration, NH3 is significantly affected by the nearest lattice oxygen, which makes the oxidative dehydrogenation reaction more likely to occur, although the adsorption energy of NH3 on Feoct-tet-terminated surface is relatively lower. These results provide a basis for understanding the interactions of NH3, NOx and O2 on Fe3O4 (1 1 1) surfaces in NH3-SCR reaction.