Catalytic reduction of NO under H2-rich and lean-burn conditions over Pd/Al2O3 and Ag-Pd/Al2O3 has been studied by temperature programmed reaction (TPR) coupled with in situ infrared (IR) and mass spectrometry (MS) techniques. Under H2-rich conditions, Pd/Al2O3 produces, Pd-NCO, Pd+-NO, Pd0-NO, and adsorbed nitrate at temperatures below 398 K. N2 and adsorbed NH3 are produced at temperatures above 400 K. Addition of Ag to Pd/Al2O3 suppresses the Pd+-NO formation and lowers the formation temperature of NH3 species to 373 K. Under lean-burn conditions, Pd/Al2O3 produces Pd-NCO, Pd+-NO, Pd0-NO, and adsorbed nitrate at temperatures below 373 K, while the addition of Ag suppresses the Pd-NCO and Pd+-NO formation, and enhances the Pd0-NO formation. Infrared results reveal that oxygen under lean-burn conditions does not oxidize Pd0 sites to Pd+ on the Ag-Pd/Al2O3 catalyst. Addition of Ag enhances NO2 formation and shifts the N2 formation to lower temperatures, suggesting that NO2 is effectively reduced to N2.
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