Sn promoted BaFeO3− catalysts for N2O decomposition: Optimization of Fe active centers

A series of BaFe1−xSnxO3−δ catalysts were prepared by sol-gel method and tested for N2O decomposition to shed light on the effect of B-site substitution on the catalytic behavior of perovskite catalysts. 119Sn and 57Fe Mossbauer results confirmed that the 5-fold coordinated Fe3+ cations with one adjacent oxygen vacancy (Fe3+ O5) were the main active centers for N2O decomposition. Doping of Sn cations can significantly improve the percentage of Fe3+ O5 from 30% (x = 0) to 68% (x = 0.8). More importantly, the valence state of Fe could be gradually reduced due to weakening of Fe O bond with increasing the Sn content, which was attributed to the stronger force of Sn than Fe in Fe O Sn structure to draw the oxygen anion and expansion of unit cell volume. Such change of Fe chemical state favored the oxygen mobility of the catalyst, leading to reduction in activation energy for N2O decomposition from ca. 241 (x = 0) to 178 kJ mol−1 (x = 0.8). BaFe0.2Sn0.8O3−δ catalyst exhibited the highest intrinsic rate of 1.49 s−1 (550 °C), nearly 4 times larger than that of BaFeO3−δ (0.43 s−1).