Effects of CO and CO2 on the desulfurization of H2S using a ZnO sorbent: a density functional theory study

Abstract

The density functional theory (DFT) method has been performed to study the effects of CO and CO₂ on the desulfurization of H₂S over a ZnO sorbent. It shows that COS is inevitably formed on the ZnO(100) surface, which tends to be adsorbed onto the surface via a S–C bond binding with either a long or a short Zn–O bond. Potential energy profiles for the COS formation via reactions between H₂S and CO, and H₂S and CO₂ on the ZnO(100) surface have been constructed. In the presence of CO, the dissociated active S of H₂S reacting with CO leads to the formation of COS, and the activation energy of the rate-determining step is 87.7 kJ mol⁻¹. When CO₂ is present, the linear CO₂ is first transferred to active CO₂ in a triplet state, and then combines with active S to form COS with the highest energy barrier of 142.4 kJ mol⁻¹. Rate constants at different temperatures show that the formation of COS via the reaction of CO and H₂S is easier than that of CO₂ and H₂S over the ZnO surface.