Reaction between carbon monoxide and nitrogen monoxide over perovskite-type mixed oxides

Abstract

Catalytic reactions between CO and NO and between CO and O₂ over several perovskite-type mixed oxides, such as LaMO₃ and La_1–xSr_xMO₃(M = Co, Fe, Mn, Cr, Ni; x= 0–0.4), have been studied in a recirculation system at 473 and 573–673 K, respectively. It has been found that the catalytic activities for the two reactions depend on the B-site element in distinctly different ways; the activity pattern for CO–NO was Cr < Mn < Fe < Co > Ni and that for CO–O₂ was Cr < Mn > Fe < Co > Ni. It was suggested that the difference of the activity pattern was due to the ability of the B-site ion to activate NO and O₂, based on the results of NO adsorption and the activity patterns reported for other oxidation reactions. The substitution of Sr²⁺ for the A site in ABO₃(A = La, B = Co, Mn, Fe) decreased monotonically the catalytic activity for the CO–NO reaction in contrast to the increase observed previously for the oxidation of propane. The order of the rate of CO–N₂O reaction was LaFeO₃ > La_0.9Sr_0.1FeO₃ > LaCoO₃ > LaMnO₃. The transformation of N₂O to N₂ over LaFeO₃ and La_0.9Sr_0.1FeO₃ in the CO–NO reaction is due to the greater rates for the CO–N₂O reaction.