The structure and NO reactivity of Zr-deposited Pd surfaces were investigated by X-ray photoelectron spectroscopy. low-energy electron diffraction. infrared reflection absorption spectroscopy, and temperature-programmed desorption. Zr oa Pd(1 0 0) was oxidized to ZrO2 by exposure to O-2 at 773 K. Heating at 823 K in a vacuum led to decomposition of ZrO2 to Zr metal and O-2. The activation energy for ZrO2 decomposition changed remarkably at Theta(zr) = 0.4. For Theta(zr) > 0.4. a hexagonal structure was observed for ZrO2/Pd(1 0 0); no ordered structure was observed for Theta(zr) < 0.4. Deposited Zr had no significant effect on the adsorption and decomposition of NO on Pd(l 0 0) but resulted in a creation of new NO dissociation sites on Pd(3 1 1). Zr on Pd(3 1 1) was oxidized to ZrOx by oxygen produced from NO dissociation. Heating at 823 K in a vacuum led to decomposition of ZrOx to Zr metal and O-2. (C) 2004 Elsevier B.V. All rights reserved.