Possible deNOx Management under Net Oxidizing Conditions: A Molecular Beam Study of 15NO + CO + O2 Reaction on Pd(111) Surfaces

Abstract

Isothermal kinetic measurements of 15NO reduction with CO on Pd(111) surfaces were carried out under net-oxidizing conditions with 15NO + CO + O2, 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 O2-rich compositions. Increasing O2 content, generally, suppresses 15NO reduction in the SS; nonetheless, irrespective of O2 content, 15N2 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 15N2:15N2O 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 → N2 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 O2-lean and -rich conditions, thus highlighting the effectiveness of 15NO reduction in TS, irrespective of the beam composition. Possibly in a future technology initiative, this aspect could be exploited to manage more 15NO reduction on Pd-based catalysts.