PALLADIUM-SUBSTITUTED LANTHANUM CUPRATES - APPLICATION TO AUTOMOTIVE EXHAUST PURIFICATION

A series of palladium-substituted La2CuO4, corresponding to the formul a La2C1-xPdxO4 (x = 0-0.2) were prepared by metal nitrate decompositio n in a polyacrylamide gel. This method allows an easy incorporation of palladium in the mixed-oxides, which are formed at moderate temperatu re with rather high specific areas (13-17 m(2)/g). The partial substit ution 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 C3H6 decreased markedl y when increasing the palladium content, the activity of catalysts La2 Cu0.9Pd0.1O4 and La2Cu0.8Pd0.2O4 being comparable to that of a Pt-Rh/C eO2-Al2O3 catalyst for NO reduction, and higher for CO and C3H6 oxidat ion. All the La2Cu1-xPdxO4 catalysts are activated under reacting cond itions. This activation corresponds to the destruction of the mixed-ox ide structure, with formation of reduced Pd-0 ions atomically disperse d, surrounded by Cu+ and Cu2+ species on a lanthanum oxycarbonate matr ix. This high dispersion state of the two transition metals in various oxidation states is supposed to originate from the initial La2Cu1-xPd xO4 structure.