The interaction of S 2 with Ag/Rh(111) and Ag/ZnO surfaces has been investigated using high-resolution photoemission spectroscopy. In general, silver “promotes” the reaction of S 2 with both clean Rh(111) and polycrystalline ZnO. On dosing Ag/Rh(111) surfaces with S 2 at 300 K, the S 2p spectra show the presence of multiple sulfur species (S, S n polymers). Annealing to 500 K decomposes the sulfur species that have significant S–S bonding and, in addition, results in the formation of metal–sulfur bonds (Rh–S and Ag–S). The formation of Rh–S bonds is indicated by a big drop in the density of states at the Fermi edge, while the formation of Ag–S bonds is evidenced by a slight positive shift (0.4 eV) and narrowing of the Ag 4d band. On Ag/Rh(111) surfaces, the rate of adsorption of S 2 is substantially larger than on Rh(111). A comparison of these results with those previously reported for the S 2/Ag/Mo(110) and S 2/Ag/Pt(111) systems indicates that Ag adatoms have the “ability” to enhance the rate of sulfidation of transition metal surfaces. On zinc oxide the Ag overlayers show a band structure that is significantly different from that of pure metallic Ag. Nevertheless, the reactivity of the Ag/ZnO surfaces towards sulfur adsorption is larger than that of pure ZnO. Ag clusters supported on ZnO react with S 2 to form AgS x species which are stable up to temperatures above 500 K. The supported Ag clusters provide a large number of electronic states that are efficient at donating electrons to the S 2(2π g) orbitals, inducing in this way the breaking of the S–S bonds and the formation of AgS x . When Ag is vapor deposited on S/ZnO surfaces, the sulfur migrates from the oxide to on-top of the Ag overlayer. This migration is favored by differences in the strength of the Ag→S and ZnO→S electron–donor interactions. Trends in the poisoning of metal/oxide catalysts by sulfur are discussed in terms of a simple mode based on perturbation theory and the Hückel or tight-binding method.