A comparison of the reaction of S2 with metallic copper, Cu2O and Cu/ZnO:: electronic properties and reactivity of copper

The adsorption of S-2 on polycrystalline copper, Cu2O and Cu/ZnO surfaces has been examined by using synchrotron-based photoemission plus INDO/S and ab initio self-consistent-held calculations. S-2 mainly interacts with the metal centers of Cu/ZnO, Cu2O and ZnO. The chemical affinity of these systems for sulfur increases following the sequence: ZnO < Cu2O < Cu/ZnO < Cu. The copper atoms in the Cu2O and Cu/ZnO systems display band structures that are substantially different from that of metallic copper, and these electronic perturbations affect their reactivity towards S-2. Once copper is bonded to oxygen on ZnO or in Cu2O, its electron density decreases, making more difficult the formation of Cu-->S-2 dative bonds and the breaking of the S-S bond. The poisoning of Cu/ZnO catalysts by sulfur is discussed in the light of these results. (C) 1998 Elsevier Science B.V. All rights reserved.