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

A series of BaFe 1− x Sn x O 3− δ catalysts were prepared by sol-gel method and tested for N 2 O decomposition to shed light on the effect of B-site substitution on the catalytic behavior of perovskite catalysts. 119 Sn and 57 Fe Mössbauer results confirmed that the 5-fold coordinated Fe 3+ cations with one adjacent oxygen vacancy (Fe 3+ O 5 ) were the main active centers for N 2 O decomposition. Doping of Sn cations can significantly improve the percentage of Fe 3+ O 5 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 N 2 O decomposition from ca. 241 ( x   =   0) to 178   kJ   mol −1 ( x   =   0.8). BaFe 0.2 Sn 0.8 O 3− δ catalyst exhibited the highest intrinsic rate of 1.49   s −1 (550   °C), nearly 4 times larger than that of BaFeO 3− δ (0.43   s −1 ).