REDUCTION OF NITRIC-OXIDE BY AMMONIA AT ATMOSPHERIC PRESSURES OVER PLATINUM POLYCRYSTALLINE FOILS AS MODEL CATALYSTS

The reduction of nitric oxide with ammonia was studied using batch-mode and flow-mode measurements in partial pressure ranges of 70-660 Pa (0.5-5 Torr) on polycrystalline platinum foils over the temperature range of 373-633 K. The reaction products observed were nitrogen, nitrous oxide, and water. Unimolecular decompositions of NO or NH3 were not detectable under these conditions, up to 773 K. The reduction of nitric oxide with ammonia occurred in the temperature range of 548-633 K. The Arrhenius curve of the reaction showed a break in the 563-603 K range, which was slightly dependent on the reactant concentrations. In this temperature range the reaction became oscillatory. The activation energies were 102 kJ/mol in the low-temperature and 212 kJ/ mol in the high-temperature ranges, respectively. The product distribution was different in the two temperature regions; in the low-temperature range the N2/N2O ratio was close to 1, while in the high-temperature regime N2 formation was dominant, and the previously formed N2O was consumed as well. © 1991.