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

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(101¯0) 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(101¯0) 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.