Catalytic activity and structural stability of La 0.9Ce 0.1Co 1− xFe xO 3 perovskite catalysts for automotive emissions control

Abstract

One of the most important issues of automotive catalysts is the endurance of fluctuations between reductive and oxidative (redox) atmospheres at high temperatures exceeding 1173 K. The catalytic activity and structural stability of La 0.9Ce 0.1Co 1− x Fe x O 3 perovskite catalysts ( x=0, 0.2, 0.4, 0.6, 0.8 and 1.0), both in powder and monolithic forms, were investigated after aging treatments in real and simulated “model” automotive exhaust gases. For powder catalysts before and after treatment both in the redox model gas and in air, the activity for oxidation of propane was evaluated and correlated with the crystal structure. For monolithic catalysts, the activities for reduction of NO, oxidations of CO and hydrocarbons (HC) were evaluated before and after aging in the flow of an engine exhaust gas at 1173 K. With increasing Co in La 0.9Ce 0.1Co 1− x Fe x O 3 perovskite catalysts, the catalytic activity increased and the structural stability decreased. La 0.9Ce 0.1Co 0.4Fe 0.6O 3 indicated the best balance of activity and durability in the automotive exhaust gas at high temperatures. When the fraction of Co exceeded 0.6, the activity diminished due to the structural transformation from perovskite to K 2NiF 4-type layered structure. These observations, in general, corresponded to the results obtained for Pd-promoted perovskite monolithic catalysts. Specifically Fe at B-site gave the durability, and Co as well as Pd improved the activity of perovskite catalysts applied to automotive emissions control.