NO oxidation activity of Ag-doped perovskite catalysts

•NO oxidation activity of LaMnO3 is enhanced by the partial substitution of Ag+ for La3+.•La1−xAgxMnO3 reveals the maximum NO oxidation rate based on the surface area at x = 0.2.•Oxygen vacancies interacted with Ag+ are the active reaction sites on La1−xAgxMnO3.•Key reaction intermediates are mono- and bi-dentate nitrates on oxygen vacancies.

Ag-doped perovskite catalysts (La1−xAgxMnO3) prepared by the citric acid method were investigated for the catalytic oxidation of NO. Compared to LaMnO3, La1−xAgxMnO3 revealed a superior NO oxidation activity with its maximum activity at x = 0.2, confirming the potential of La0.8Ag0.2MnO3 as one of the most promising NO oxidation catalysts. The high reactivity of La0.8Ag0.2MnO3 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 La1−xAgxMnO3 has been postulated on the basis of the redox process involving the oxygen vacancy, oxygen, NO, NO2 and NO3.

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