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

The regeneration mechanisms of sulfurized alpha-Fe2O desulfurization sorbent under O-2 atmosphere are systematically studied by density functional theory (OFT) 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 O-2 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 alpha-Fe2O(0001) surface can be repaired under O-2 atmosphere, and the reparation mechanism demonstrates that the dissociation of 02 on the O-vacancy alpha-Fe2O(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 alpha-Fe2O(0001) surface can accelerate the dissociation of O-2, which is favorable to the regeneration of sulfurized surfaces. (C) 2014 Elsevier B.V. All rights reserved.