The regeneration mechanisms of sulfurized α-Fe2O3 surfaces under O2 atmosphere: A density functional theory study

The regeneration mechanisms of sulfurized α-Fe2O3 desulfurization sorbent under O2 atmosphere are systematically studied by density functional theory (DFT) slab calculation. The regeneration pathways are proposed for two sulfurized surfaces, “S-contained surface” and “S-adsorbed surface”, which are derived from the substitution of surface O atom by S atom and the adsorption of S atom on the surface Fe atom, respectively. Our results show that two competitive regeneration pathways exist on each sulfurized surface. For the regeneration on the S-contained surface and the S-adsorbed surface, the rate-determining step is the dissociation of O2 with the energy barriers of 136.7 and 227.3 kJ·mol− 1, respectively, suggesting that the regeneration on the S-contained surface is easier than that on the S-adsorbed surface. Then, the O vacancy on the α-Fe2O3(0001) surface can be repaired under O2 atmosphere, and the reparation mechanism demonstrates that the dissociation of O2 on the O-vacancy α-Fe2O3(0001) surface only needs to overcome a lower energy barrier of 49.8 kJ·mol− 1 than those (136.7 and 227.3 kJ·mol− 1) on two sulfurized surfaces. As a result, the presence of O vacancy on the α-Fe2O3(0001) surface can accelerate the dissociation of O2, which is favorable to the regeneration of sulfurized surfaces.