Effect of Ag addition on the thermal stability and catalytic properties of LaFeO₃ perovskite

The effect of low Ag substitution in LaFeO₃ perovskite on the thermal stability and catalytic oxidation of toluene was studied. Perovskites of the type La_1-xAg_xFeO₃ (x_Ag=0.0, 0.05, 0.10) were prepared by the amorphous citrate method; characterized by nitrogen adsorption, XRD, FTIR, SEM-EDAX, TPR and O₂-TPD techniques; and tested for the catalytic combustion of toluene in a flow reactor under excess oxygen. In comparison with the pure perovskite LaFeO₃, the partially substituted La_1-xAg_xFeO₃ present a perovskite structure with well-defined crystalline phases and greater reduction ability (attributable to the redox pair Fe⁺³/Fe⁺⁴). Noticeable changes in the α and β-oxygen contents upon silver substitution were detected. Larger content of α-oxygen in the pure LaFeO₃ perovskite is associated with greater catalytic activity. Two important effects upon Ag substitution in a pure LaFeO₃ perovskites were observed: i) a greater reduction ability, ii) higher occurrence of oxygen vacancies due to β-oxygen desorption, which were not active in the studied reaction.