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

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 SrFe1-xTixO3-delta-supported Pd catalysts exhibit high catalytic activities for NO reduction with C3H6 and CO in the presence of O-2, 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/SrFe0.2Ti0.8O3-delta among the examined catalysts. The state of the loaded Pd species can be controlled by the Fe/(Fe + Ti) ratio in SrFe1-xTixO3-delta, and highly active PdO nanoparticles are properly anchored on SrFe0.2Ti0.8O3-delta. The Tirich Pd/SrFe0.2Ti0.8O3-delta shows significantly higher catalytic activity and is more thermally stable than the conventional Pd/Al2O3, which has a high surface area. Since Fe-rich SrFe1-xTixO3-delta has the high 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/SrFe0.8Ti0.2O3-delta retains its high NO-reduction activity for longer times even under oxidative conditions, when compared to SrFeO3-delta or Ti-rich Pd/SrFe1-xTixO3-delta. The oxygen storage properties of Pd/SrFe0.8Ti0.2O3-delta allow it to effectively act as an oxygen buffer for NO reduction. These properties ensure that the SrFe1-xTixO3-delta support, with both high thermal stability and oxygen storage capacity, is a very useful environmental-catalyst material.