Low-temperature NH3-SCR of NO by lanthanum manganite perovskites: Effect of A-/B-site substitution and TiO2/CeO2 support

• A positive effect of perovskite structure of LaMnO3 for NH3-SCR of NO was found.
• SCR activity could be further improved via A/B-site substitution and oxide support.
• Ideal performance associates with facilitating NO oxidation or depressing adNOx.
• Monodentate nitrate is reactive with adNH3, while ionic nitrate is totally inert.

A series of LaMn-based perovskites was fully characterized and tested for the selective catalytic reduction (SCR) of NO by NH3 in the presence of O2. The physicochemical properties, adsorbed species and surface reaction were investigated by means of N2 sorption, XRD, XPS, H2-TPR, NO + O2- or NH3-TPD, and in situ DRIFTS, in order to discriminate the effects of A- or B-site partial substitutions and their supports on SCR performances. With respect to the parent material, cation incorporation and support dispersion achieved the different enhancements in deNOx activity, mainly due to their modifications in nitrites/nitrates and adNH3 cumulants as well as redox capacity. For these prepared samples, an inhibition on the coverage of inert ionic nitrates was thought to be crucial to improve NO conversion at the high-temperature zone; while an increase in NO oxidation ability was considered to be important at temperatures below 200 °C, as observed over LaMnO3/CeO2. Besides, perovskite structure was apparently beneficial for this SCR process via largely enriching the surface manganese and oxygen species.

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