Abstract
A series of palladium-substituted La 2CuO 4, corresponding to the formula La 2Cu 1 − x Pd x O 4 ( x = 0−0.2) were prepared by metal nitrate decomposition in a polyacrylamide gel. This method allows an easy incorporation of palladium in the mixed-oxides, which are formed at moderate temperature with rather high specific areas (13–17 m 2/g). The partial substitution of copper for palladium allows a strong improvement of the three-way catalytic activity, in particular for NO reduction. The light-off temperatures for the conversions of CO, NO and C 3H 6 decreased markedly when increasing the palladium content, the activity of catalysts La 2Cu 0.9Pd 0.1O 4 and La 2Cu 0.8Pd 0.2O 4 being comparable to that of a Pt-Rh/CeO 2–Al 2O 3 catalyst for NO reduction, and higher for CO and C 3H 6 oxidation. All the La 2Cu 1 − x Pd x O 4 catalysts are activated under reacting conditions. This activation corresponds to the destruction of the mixed-oxide structure, with formation of reduced Pd 0 ions atomically dispersed, surrounded by Cu + and Cu 2+ species on a lanthanum oxycarbonate matrix. This high dispersion state of the two transition metals in various oxidation states is supposed to originate from the initial La 2Cu 1 − x Pd x O 4 structure.
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