The interaction of S-2 with Ag/Al2O3 and Zn/Al2O3 surfaces has been investigated using thermal desorption mass spectroscopy, core- and valence-level photoemission, and ab initio self-consistent-field calculations. The sticking coefficient of S-2 On clean alumina is small (<0.1) at temperatures between 300 and 700 K. In the S-2/Al2O3 system, there is an energy mismatch between the orbitals of the molecule and the bands of the oxide, and the reactivity of S-2 On pure alumina is very low. The adsorption of sulfur on Ag/Al2O3 and Zn/Al2O3 surfaces induces strong perturbations in the electronic properties of the admetals and oxide support. In the Ag/Al2O3 and Zn/Al2O3 systems, the supported metal clusters (or particles) provide a large number of electronic states that are very efficient at donating charge into the S-2(2 pi g) orbitals, inducing in this way the breaking of the S-S bond and the formation of admetal sulfides (AgSx and ZnSy). The larger the electron transfer from the supported metal into the S-2(2 pi g) orbitals, the bigger the adsorption energy of the molecule and the easier the cleavage of the S-S bond. The AgS, and ZnS, species decompose at temperatures between 750 and 900 K following two different reaction pathways : AgSx,solid --> S-2,S-gas + Ag-solid and ZnSy,solid --> S-2,S-gas + Zn-gas.