Photoemission, thermal desorption spectroscopy and density-functional calculations were used to study the chemistry Of SO2 on Au nanoparticles supported on MgO(1 0 0). The heat of adsorption of the molecule on the Au nanoparticles is similar to 15 kcal/mol compared to 8 kcal for SO2 on Au(I 11). corner sites in the An nanoparticles are responsible for this difference in reactivity. The dissociation Of SO2 on Au/MgO(1 0 0) is very limited due to weak Au <----> MgO interactions. A comparison of the behavior of SO2 on Au/MgO(1 0 0) and Au/TiO2(110) shows how important can be the effects of the oxide support for the activation of An nanoparticles. (C) 2003 Elsevier B.V. All rights reserved.