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

Abstract

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 NH 3 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 Pd 2+ species being more reactive than the Pd 4+ species. In-situ Raman analysis demonstrated that NH 3 oxidation proceeded through the reduction of PdOx by NH 3 , 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 NH 3 tends to dehydrogenate and dimerize to form *NH 2 −NH 2 species, which successively dehydrogenate to produce N 2 .

Source identification of ultrafine particulate matter and ammonia emissions in the metropolitan area

“…In particular, managing ammonia is crucial because it reacts with nitric and sulfuric acids in the atmosphere to form secondary aerosols such as ammonium nitrate [NH 4 NO 3 ] and ammonium sulfate [[NH 4 ] 2 SO 4 ], the main components of PM 2.5 [21,22]. Ammoniated aerosols worsen urban air quality and affect human health [23][24][25].…”