Efficient oxygen storage property of Sr–Fe mixed oxide as automotive catalyst support

Abstract

The efficiency of catalytic systems for the removal of nitrogen oxides (NO_x) from automotive exhaust gases is strongly affected by the oxygen concentration in the exhaust gas. To overcome this problem, an oxygen storage material has been used in the purification systems. This study demonstrates the NO reduction under various oxygen concentrations over Pd/Sr₃Fe₂O_7−δ catalysts in which Fe is partially replaced by other transition metals (Mn, Co, Ni, and Cu). Pd/Sr₃(Fe_0.8Ni_0.2)₂O_7−δ with a layered perovskite structure showed the highest NO reduction activity among the examined catalysts under a wide range of oxygen concentrations. Ni³⁺ was found to replace Fe³⁺ rather than Fe⁴⁺ in Sr₃Fe₂O_7−δ. Pd/Sr₃(Fe_0.8Ni_0.2)₂O_7−δ showed significantly improved oxygen storage capacity as compared to Pd/Sr₃Fe₂O_7−δ, which was attributed to the redox between Ni³⁺ and Ni²⁺ accompanying the Fe⁴⁺/Fe³⁺ redox reaction during oxygen release/storage processes. This study provides useful information for the design of novel catalysts with a perovskite-type structure.