Performance of Modified La xSr1- xMnO3 Perovskite Catalysts for NH3 Oxidation: TPD, DFT, and Kinetic Studies.

The modified perovskites (La xSr1- xMnO3) were prepared using the selective dissolution method for the selective catalytic oxidation (SCO) of NH3. We found that more Mn4+ cations and active surface oxygen species formed on the catalyst's surface with increasing the dissolution time (dis). The 1h-dis catalyst exhibited excellent NH3 conversion, and it performed well in the presence of SO2 and H2O. The 10h-dis and 72h-dis catalysts produced considerable N2O and NO at high temperatures, while they were not detected from the fresh catalyst. Both temperature-programmed experiments and density functional theory calculations proved that NH3 strongly and mostly bonded to the B-site cations of the perovskite framework rather than A-site cations: this framework limited the bonding of SO2 to the surface. The reducibility increased superfluously after more than 10 h of immersion. The adsorptions of NH3 on Mn4+ exposed surface were stronger than that on La3+ or Sr4+ exposed surfaces. The selective catalytic reduction, nonselective catalytic reduction, and catalytic oxidation reactions all contributed to NH3 conversion. The formed NO from catalytic oxidation preferred to react with -NH2/-NH to form N2/N2O.