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Performance of Modified LaxSr1–xMnO3 Perovskite Catalysts for NH3 Oxidation: TPD, DFT, and Kinetic Studies
- Wang, Dong, Peng, Yue, Yang, Qilei, Xiong, Shangchao, Li, Junhua, Crittenden, John
- Environmental science & technology 2018 v.52 no.13 pp. 7443-7449
- adsorption, ammonia, catalysts, cations, density functional theory, environmental science, lanthanum, manganese, nitric oxide, nitrous oxide, oxidation, oxygen, sulfur dioxide, temperature
- 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 N₂/N₂O.