Theoretical investigation of H2S removal on γ-Al2O3 surfaces of different hydroxyl coverage

Abstract

The sulfurized processes of H₂S on dehydrated (100) and (110) as well as partially hydrated (110) surfaces of γ-Al₂O₃ were investigated using a periodic density functional theory method. The adsorption configurations of possible intermediates and the potential energy profiles of reaction are depicted. Our results show that H₂S adsorbs preferentially on the Al site along with the S bond, and the adsorption energies are −32.52 and −114.38 kJ mol⁻¹ on the dehydrated (100) and (110) surfaces, respectively. As the reaction temperature of the desulfurization changes, the (110) surface presents different levels of hydroxyl coverage, which affects the adsorption structures of species and reaction energies of dissociation processes. The bonding strengths of H₂S on the partially hydrated (110) surfaces are weaker than on the dehydrated (110) surface. Compared with the 3.0 and 8.9 OH per nm² surfaces, the H₂S has the weakest adsorption energy (−39.85 kJ mol⁻¹) and the highest activation energy (92.06 kJ mol⁻¹) on the 5.9 OH per nm² surface. On the 8.9 OH per nm² surface, the activation energy of the second dissociation step (rate-determining step) for H₂S dissociation is merely 38.32 kJ mol⁻¹. On these involved surfaces, cleavage processes of the two H–S bonds present facile activation energies, which are facilitative to desulfurization.