Possible deNO<SUB>x</SUB> management under net oxidizing conditions: a molecular beam study of <SUP>15</SUP>NO + CO + O<SUB>2</SUB> reaction on Pd(111) surfaces

Isothermal kinetic measurements of <SUP>15</SUP>NO reduction with CO on Pd(111) surfaces were carried out under net-oxidizing conditions with <SUP>15</SUP>NO + CO + O<SUB>2</SUB>, using a molecular beam instrument (MBI). Transient state (TS) and steady state (SS) kinetic details of the above reaction were obtained for a wide range of temperature and beam compositions, especially with O<SUB>2</SUB>-rich compositions. Increasing O<SUB>2</SUB> content, generally, suppresses <SUP>15</SUP>NO reduction in the SS; nonetheless, irrespective of O<SUB>2</SUB> content, <SUP>15</SUP>N<SUB>2</SUB> was produced in TS, and to a significant extent under SS conditions too. Sustainable N2 production between 450 and 600 K and with low to moderate amount of oxygen was observed, and the extent of NO decomposition was also quantified. The ratio of <SUP>15</SUP>N<SUB>2</SUB>:<SUP>15</SUP>N<SUB>2</SUB>O was generally found to be around 8:1 under most of the reaction conditions. Maxima in the SS reaction rates of all products were observed between 500 and 600 K. Compared to other elementary reaction steps, a slow decay observed with N + N → N<SUB>2</SUB> step under SS beam oscillation conditions demonstrates its contribution to the rate limiting nature of the overall reaction. Fast beam switching experiments have been performed alternately between O<SUB>2</SUB>-lean and -rich conditions, thus highlighting the effectiveness of <SUP>15</SUP>NO reduction in TS, irrespective of the beam composition. Possibly in a future technology initiative, this aspect could be exploited to manage more <SUP>15</SUP>NO reduction on Pd-based catalysts