Efficient Reduction of NOx by H2 Under Oxygen-Rich Conditions over Pd/TiO2 Catalysts: An in situ DRIFTS Study

The H2/NO/O2 reaction under lean-burn conditions has been studied by means of in situ DRIFTS, reactor measurements and temperature-programmed desorption with the aim of understanding the very different behavior of Pd/TiO2 and Pd/Al2O3 catalysts. The former deliver very high NOx conversions (70-80%) with good N2 selectivity whereas the latter show very low activity. In addition, PdTiO2 exhibits two distinct NOx reduction pathways, thus greatly extending the useful temperature range. It is shown that the PdTiO2 low-temperature channel involves adsorption and subsequent dissociation of NO on reduced (Pd0) metal sites. The low activity of PdAl2O3 is a consequence of palladium remaining in an oxidized state under reaction conditions. The high-temperature NO reduction channel found with PdTiO2 is associated with the generation and subsequent reaction of NHx species.