Model catalytic studies under ambient conditions require materials with well-defined structures for the establishment of clear relationships between structural and catalytic properties. In the present work, such a system was prepared by controlled decomposition of organometallic Pd precursors on a MgO support. The resulting Pd nanoparticles of highly defined morphology were characterized by high-resolution transmission electron microscopy and investigated with respect to their interaction with CO, O-2, and H-2 by IR spectroscopy (DRIFTS). Temperature-dependent CO adsorption experiments revealed the available adsorption sites on the Pd particles and indicated CO disproportionation on the Pd particles. We report in particular on the interplay between metal and support in these processes, which was analyzed by a thorough comparison of Pd/MgO with the pure MgO support. Investigations of the interaction with CO and H-2 suggest that Pd facilitates the formation of formates on MgO via dissociation of hydrogen on the Pd particles. Furthermore, CO oxidation was studied as a function of the CO/O-2 ratio in the temperature range 100-150 degrees C. (C) 2007 Elsevier Inc. All rights reserved.