Characterization of alumina supported Pd catalysts modified by rare earth oxides using X-ray photoelectron spectroscopy and X-ray diffraction:: enhanced thermal stability of PdO in Nd/Pd catalysts

Thermal stability of palladium oxides on industrially manufactured alumina supported catalysts modified by Nd, La and Ba oxides was investigated using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Catalysts were prepared by mechanical mixing of washcoat material with Pd precursor compound. A stepwise thermal reduction in high Vacuum was performed in order to investigate the effect of noble metal loading, stabilizers and aging on the thermal stability of PdO. One of the pseudo-binary compounds of Nd2O3/PdO, Nd4PdO7, was successfully manufactured and characterized by XRD and XPS, The presence of Nd4PdO7 as a surface compound was identified by its unusually high binding energy of the Pd 3d(5/2) photoelectron peak (337.6 eV). PdO formed as a result of the decomposition of the alumina supported Nd4PdO7 upon aging in air at 950 degreesC exhibited clearly higher thermal stability than pure PdO supported on alumina. La, Ba and Nd oxides were also found to enhance the thermal stability of PdO. (C) 2001 Elsevier Science B.V. All rights reserved.