Characteristics of Pt/WO3/CeO2/ZrO2 catalysts for catalytic reduction of NO by CO

Various supported Pt catalysts (Pt/WO3/CeO2/ZrO2; Pt/ZrO2, Pt/CeO2, Pt/CeZrO, Pt/WO3/ZrO2, and Pt/WO3/CeZrO) were prepared and characterized, and their characteristics of catalytic reductions of NO by CO with or without oxygen were investigated. TPR and CO-TPD showed that Pt/CeO2 and Pt/CeZrO could be easily reduced by CO while the reduction by CO was inhibited with the introduction of WO3 in the case of Pt/WO3/CeZrO. According to NO-TPD, NO reduction could not proceed over the catalysts (Pt/WO3/CeZrO, Pt/ZrO2, Pt/WO3/ZrO2) to remain in an oxidized state even after reduction by CO, but NO reduction was possible over Pt/CeO2 and Pt/CeZrO catalysts when reduced by CO. For NO+CO reaction without oxygen, those easily reducible catalysts (Pt/CeO2 and Pt/CeZrO) exhibited better catalytic performances. With excess oxygen, however, Pt/WO3/CeZrO and Pt/WO3/ZrO2 catalysts exhibited higher NO conversions to N2 and N2O especially at a low temperature. The acidity from ZrO2 and WO3 in Pt/WO3/CeO2/ZrO2 catalysts should play an important role on their NO conversion only in the presence of excess oxygen.