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

The modified perovskites (La x Sr 1– x MnO 3 ) were prepared using the selective dissolution method for the selective catalytic oxidation (SCO) of NH 3 . We found that more Mn 4+ cations and active surface oxygen species formed on the catalyst’s surface with increasing the dissolution time (dis). The 1h-dis catalyst exhibited excellent NH 3 conversion, and it performed well in the presence of SO 2 and H 2 O. The 10h-dis and 72h-dis catalysts produced considerable N 2 O 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 NH 3 strongly and mostly bonded to the B-site cations of the perovskite framework rather than A-site cations: this framework limited the bonding of SO 2 to the surface. The reducibility increased superfluously after more than 10 h of immersion. The adsorptions of NH 3 on Mn 4+ exposed surface were stronger than that on La 3+ or Sr 4+ exposed surfaces. The selective catalytic reduction, nonselective catalytic reduction, and catalytic oxidation reactions all contributed to NH 3 conversion. The formed NO from catalytic oxidation preferred to react with −NH 2 /–NH to form N 2 /N 2 O.