DRIFTS study of NO–H2 reaction over Pd/Al2O3 with excess oxygen

Pd (0.1 wt.%)/Al2O3 catalyst was found to be active for the selective NO reduction employing H2 (NO conversion>90%) under excess O2 at low temperatures (110–190 °C) with good N2 selectivity (about 70%). The selectivity towards N2O was sensitive to the reaction conditions and decreased as the temperature was raised. The maximum selectivity to NH3 occurred at 190 °C. The selectivity to N2O was inhibited greatly by O2 at low temperatures. Gaseous O2 promoted the selectivity to N2 as well as the generation of adsorbed NH species in comparison to the reactions without O2. In situ diffuse reflectance IR spectroscopy (DRIFTS) measurements suggested that there was competition between H2 and other adsorbed species such as nitrates and water at low temperatures, and the rate determining step may be the adsorption and activation of H2 over the catalyst.