Performance of Modified LaxSr1-xMnO3 Perovskite Catalysts for NH3 Oxidation: TPD, DFT, and Kinetic Studies

The modified perovskites (LaxSr1-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 N-2/N2O.