Three-way Catalysis with Noble Metal-Substituted La(Fe,Co)O3 Perovskites - the Role of Noble and Base Metal Components

Kurzfassung

La(FexCo1-x)O3 perovskites with noble metals incorporated (Pd in different amounts, Pt, Rh; with Pd at x = 1, 0.7, 0) were prepared via the dry citrate method and examined with respect to their behavior in three-way catalysis (lean and stoichiometric model feeds containing CO, propene, NO, and O2) in the as-prepared state and after redox stress of different severity (at temperatures up 1173 K). Results were compared with data obtained with a commercial Pd-based three-way catalyst. Perovskites outperformed the reference in CO oxidation but were less active in propene oxidation and NO reduction. While their oxidation activity was rather stable, their NO reduction activity suffered severely from the redox treatments unlike that of the reference. It was concluded that oxidation and reduction reactions are catalyzed by different sites. While the presence and the nature of the noble metal were mostly irrelevant for oxidation reactions, in particular for CO oxidation, NO reduction was dominated by the contribution of the noble metal component. The inferior NO reduction activity despite noble metal contents of up to 2.5 wt% and the dominance of the perovskite surface in propene oxidation (compared with high oxidation activity of Pd in the reference catalyst) suggest that the metal component was not well exposed in the perovskite catalysts.