Exploring the Impact of Palladium Species’ State on Catalytic Ammonia Elimination over Palladium Catalysts

Supported palladium catalysts are widely employed in ammonia catalytic oxidation, while the active sites and reaction mechanism involved remain debated. The present work validated that metallic Pd nanoparticles were highly reactive in catalyzing NH3 oxidation at low temperatures, but maintaining their stability under working conditions is a significant challenge. Stable PdOx nanoparticles exhibited high reactivity in this reaction, with the Pd2+ species being more reactive than the Pd4+ species. In-situ Raman analysis demonstrated that NH3 oxidation proceeded through the reduction of PdOx by NH3, followed by the activation of oxygen on the reduced Pd species, resulting in the restoration of the PdOx species. A significant transition in the rate-determining step occurred as the reaction temperature increased, shifting from the reoxidation of Pd to the reduction of PdOx. Operando DRIFTS-MS and DFT calculations suggested that NH3 tends to dehydrogenate and dimerize to form *NH2–NH2 species, which successively dehydrogenate to produce N2.