Catalytic NO reduction with CO on La1−xSrx(Fe3+/Fe4+)O3±δ perovskite-type mixed oxides (x = 0.00, 0.15, 0.30, 0.40, 0.60, 0.70, 0.80, and 0.90) Original Research Article

Eight (8) perovskite-type mixed oxides having the general formula La1−xSrxFeO3±δ (x=0, 0.15, 0.3, 0.4, 0.6, 0.7, 0.8 and 0.9) were prepared using the corresponding nitrate salts and heating at 1000 °C. As determined by Mössbauer spectroscopy the gradual substitution of La by Sr results in transformation of Fe3+ in the solids to Fe4+ existing in the perovskite structure SrFe4+O3. Other crystal phases detected by XRD include LaFeO3 and Fe2O3. The solids were tested for their catalytic activity for the reaction NO+CO→products in a lab-scale plug flow reactor (PFR) between 250 and 580 °C. The most active solids are the ones possessing the lowest amount of Fe4+ and the highest amount of Fe3+. The reaction rate for the NO and CO elimination decreases as the difference δ(−ΔHM−O)=∑(−ΔHM−O)Fe3+,Fe4+−∑(−ΔHM−O)Fe3+ increases, where ∑(−ΔHM−O)Fei+ is the sum of enthalpies of the M–O bonds of the nominal solids containing Fei+ (i=3, 4) iron species.