THE REDUCTION OF NITRIC-OXIDE BY AMMONIA OVER POLYCRYSTALLINE PLATINUM MODEL CATALYSTS IN THE PRESENCE OF OXYGEN

The reaction system of nitric oxide, ammonia, and oxygen was studied using batch-mode measurements in partial pressure ranges of 65-1000 Pa (0.5-7.6 Torr) on polycrystalline Pt foils over the temperature range 423-598 K. Under these conditions the oxidation of nitric oxide was not detectable. The ammonia oxidation reaction, using dioxygen, occurred in the temperature range 423-493 K, producing nitrogen and water as the only products. The activation energy of the nitrogen formation was found to be 86 kJ/mol. Above this temperature range, flow-mode measurements showed the formation of both nitrous oxide and nitric oxide. The reaction rate betwen ammonia and oxygen was greatly decreased (about a factor of 10) by nitric oxide, while the reaction rate between nitric oxide and ammonia was accelerated (about 10-fold) due to the presence of oxygen. Nitric oxide reduction by ammonia in the presence of oxygen occurred in the temperature range 423-598 K. The products of the reaction were nitrogen, oxygen, nitrous oxide, and water. The Arrhenius plot of the reaction showed a break near 523 K. Below this temperature the activation energy of the reaction ws 13 kJ/mol, and in the higher-temperature range it was 62 kJ/mol. At 473 K, the N2/N2O ratio was about 0.6 and O2 formation was also monitored. At 573 K, the N2/N2O ratio was approximately 2 and oxygen was consumed in the course of the reaction as well. © 1992.