Catalytic behaviour of La4PdO7 based catalysts when exposed to car exhaust conditions

The catalytic properties of ex situ prepared La4PdO7 were studied under automotive exhaust conditions. Monophasic La4PdO7 was deposited onto gamma-Al2O3 coated cordierite monoliths and light-off curves were recorded under oxidising and reducing conditions. Initially the catalytic activity for oxidation of CO and C3H6 and reduction of NO was low but after the catalyst had been exposed to a reducing atmosphere of simulated car exhaust composition at 600 degrees C a three-way catalytic behaviour was obtained with a T-50 value of about 340 degrees C. Using oxidising conditions and a similar activation procedure, a catalyst with CO and C3H6 oxidation activity (T-50 = 405 degrees C) but minor activity for reduction of NO was obtained. This behaviour is interpreted in terms of La4PdO7 being decomposed and nanosized PdO particles being formed; these in turn are reduced to Pd and Pd is the catalytically active component in the catalyst. These conclusions are supported by X-ray diffraction, infrared spectroscopy, scanning and transmission electron microscopy studies combined with element analysis of freshly prepared and thermally activated catalysts.