NO oxidation activity of Ag-doped perovskite catalysts

Ag-doped perovskite catalysts (La_1-xAg_xMnO₃) prepared by the citric acid method were investigated for the catalytic oxidation of NO. Compared to LaMnO₃, La_1-xAg_xMnO₃ revealed a superior NO oxidation activity with its maximum activity at x = 0.2, confirming the potential of La_0.8Ag_0.2MnO₃ as one of the most promising NO oxidation catalysts. The high reactivity of La_0.8Ag_0.2MnO₃ is mainly due to the high oxygen vacancy concentration on its surface produced by the partial substitution of La³⁺ with Ag⁺ in LaMnO₃, as determined by the XRD, SEM, XPS, O₂-TPD, H₂-TPR, (NO + O₂)-TPRD and DRIFT studies. The mono- and bi-dentate nitrates formed on the oxygen vacancies of perovskite appear to be the primary reaction intermediates for the NO oxidation reaction over the Ag-doped perovskite catalyst. A plausible reaction pathway of the NO oxidation over La_1-xAg_xMnO₃ has been postulated on the basis of the redox process involving the oxygen vacancy, oxygen, NO, NO₂ and NO₃.