Effect of Promoter on NO Selective Catalytic Reduction over Pd/γ-Al2O3 Catalysts

The effect of alkaline metal, alkaline-earth metal or rare-earth oxides doping to Pd/γ-Al2O3on the properties of palladium supported catalysts was investigated. It is confirmed that CeO2 and Li2O promoterscan improvesignificantly the activitiesof palladiumsupported catalystsfortheselective reduction of NO with propene in oxidizing atmosphere, and increase the maximum conversions of NO by afactor of 2~4.5. From XRD analysis, Pd/CeO2-Al2O3and Pd/Li2O-Al2O3have the higher Pd dispersion than theothersamples. TPDforNOand O2simultaneousadsorptionon the catalystswere detected by a mass spectrometer, and the results indicate that there are the stronger dissociation adsorption of NO on Pd/CeO2-Al2O3and Pd/Li2O-Al2O3. It is also discussed that the formation of surface adsorption species such as NO, N2O, NO2-and NO3and their desorption properties influence the activities of catalysts for NO selective reduction.