In situ infrared study of NO reduction over Pd/Al2O3 and Ag-Pd/Al2O3 catalysts under H2-rich and lean-burn conditions

Catalytic reduction of NO under H-2-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 H-2-rich conditions, Pd/Al2O3 produces, Pd-NCO, Pd+-NO, Pdo-NO, and adsorbed nitrate at temperatures below 398 K. N-2 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, Pdo-NO, and adsorbed nitrate at temperatures below 373 K, while the addition of Ag suppresses the PdNCO and Pd+-NO formation, and enhances the Pdo-NO formation. Infrared results reveal that oxygen under lean-burn conditions does not oxidize Pdo sites to Pd+ on the Ag-Pd/Al2O3 catalyst. Addition of Ag enhances NO2 formation and shifts the N-2 formation to lower temperatures, suggesting that NO2 is effectively reduced to N-2. (C) 2009 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.