Catalytic activity and structural stability of La0.9Ce0.1Co1-xFexO3 perovskite catalysts for automotive emissions control

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 La0.9Ce0.1Co1-x FexO3 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 La0.9Ce0.1Co1-x FexO3 perovskite catalysts, the catalytic activity increased and the structural stability decreased. La0.9Ce0.1Co0.4Fe0.6O3 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 K2NiF4-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. (C) 2002 Elsevier Science B.V. All rights reserved.