The influence of nonstoichiometry on LaMnO3 perovskite for catalytic NO oxidation

A series of structural modified LaxMnO3 (x = 0.9, 0.95, 1, 1.05, 1.11) perovskites used for NO oxidation was synthesized by a sol–gel method and characterized by XRD, BET, XPS, EPR and H2-TPR. La0.9MnO3 sample exhibits superior activity, and a 50% NO conversion at 250 °C is obtained. XPS and EPR results reveal a higher Mn4+/Mn3+ ratio in Mn-rich samples, which induce more active oxygen bonding to Mn4+ due to the need for balancing the chemical states and stabilizing the structure. Easily regenerated oxygen associated with Mn4+ catalyzes the low-temperature NO oxidation. The constant activation energy (44.8 kJ/mol) obtained in the kinetics tests indicates the same mechanism of NO oxidation operated on all the samples.

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► The LaxMnO3 (x = 0.9, 0.95, 1, 1.05, 1.11) perovskites are applied as catalysts for NO oxidation to NO2.
► Phase transition of crystal system appears by nonstoichiometry in LaMnO3.
► The Mn4+ content increases with lower La/Mn ratio (x value).
► The same mechanism of NO oxidation over the La-Mn-O perovskites is observed.
► The oxygen species associated with modified Mn4+/Mn3+ sites of the La-Mn-O perovskites catalyzes the low temperature NO oxidation.