electrocatalytic reduction of 0.5 M nitrate in 1 M HClO4 over carbon-supported palladium nanoparticles (mean size 10.5 nm) was studied with differential electrochemical mass spectrometry (DEMS) as a function of reaction temperature between 0 and 55 C. The palladium nanoparticles are active for the electrocatalytic reduction of nitrate as evidenced by the detection of N2O and NO in DEMS. NO is produced during the anodic scan between 0.8 and 1.0 V vs reversible hydrogen electrode (RHE) and also during the cathodic scan between 0.3 and 0.0 V vs RHE. In contrast, N2O is only produced during the cathodic scan between 0.4 and 0.0 V vs RHE. While the reduction of NO3- to NO and N2O during the cathodic scan occurs only at significant overpotentials, the required overpotential decreases with increasing temperature. The potential dependencies of the apparent activation energies for the cathodic NO and N2O production indicate that at potentials above 0.1 and 0.075 V vs RHE, the respective kinetics of NO and N2O evolution are primarily determined by the potential. At potentials below 0.1 and 0.075 V vs RHE, respectively, the apparent activation energies for the evolution of NO and N2O are largely potential independent. (c) 2007 The Electrochemical Society.