Model studies carried out on ultrahigh vacuum (UHV) prepared nanoparticles grown on well-ordered oxide surfaces allow insight into structure and reactivity of such systems at the atomic level. We review work on hydrogenation reactions of hydrocarbons on I'd metal particles. addressing in particular the question of structure sensitivity and in a second example the preparation and characterization of supported vanadia monolayer catalysts for oxidation reactions. In the latter case we address the vibrational properties of vanadia "monolayer model catalysts" on alumina and on silica. (c) 2005 Elsevier B.V. All rights reserved.