Pd/SrFe1–xTixO3−δ as Environmental Catalyst: Purification of Automotive Exhaust Gases

Abstract

Environmental catalysts are required to operate highly efficiently under severe conditions in which they are exposed to reductive and oxidative atmospheres at high temperatures. This study demonstrates that SrFe_1-xTi_xO_3-δ-supported Pd catalysts exhibit high catalytic activities for NO reduction with C₃H₆ and CO in the presence of O₂, which is a model reaction for the purification of automotive exhaust gases. Catalytic activity is enhanced with increasing Ti content, and the highest activity is observed for Pd/SrFe_0.2Ti_0.8O_3-δ among the examined catalysts. The state of the loaded Pd species can be con-trolled by the Fe/(Fe+Ti) ratio in SrFe_1-xTi_xO_3-δ, and highly active PdO nanoparticles are properly anchored on the SrFe_0.2Ti_0.8O_3-δ. The Ti-rich Pd/SrFe_0.2Ti_0.8O_3-δ shows significantly higher catalytic activity and is more thermally stable than the conventional Pd/Al₂O₃, which has a high surface area. Since Fe-rich SrFe_1-xTi_xO_3-δ has high the oxygen storage capacity, its response capabilities to atmospheric fluctuations were evaluated by changing the oxygen concentration during NO reduction. As a result, Fe-rich Pd/SrFe_0.8Ti_0.2O_3-δ retains its high NO-reduction activity for longer times even under oxidative conditions, when compared to SrFeO_3-δ or Ti-rich Pd/SrFe_1-xTi_xO_3-δ. The oxygen storage properties of Pd/SrFe_0.8Ti_0.2O_3-δ allow it to effectively act as an oxygen buffer for NO reduction. These properties ensure that the SrFe_1-xTi_xO_3-δ support, with both high thermal stability and oxygen storage capacity, is a very useful environmental-catalyst material.