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). Cataly sts were prepared by mechanical mixing of washcoat material with Pd precurs or compound. A stepwise thermal reduction in high Vacuum was performed in o rder to investigate the effect of noble metal loading, stabilizers and agin g on the thermal stability of PdO. One of the pseudo-binary compounds of Nd 2O3/PdO, Nd4PdO7, was successfully manufactured and characterized by XRD an d 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 e V). PdO formed as a result of the decomposition of the alumina supported Nd 4PdO7 upon aging in air at 950 degreesC exhibited clearly higher thermal st ability 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.