XPS and TPR examinations of γ-alumina-supported Pd-Cu catalysts

Alumina-supported palladium-copper catalysts, which promote liquid-phase nitrate reduction, have been prepared according to different impregnation sequences of gamma -Al2O3 support and characterized by X-ray photoelectron spectroscopy (XPS), X-ray induced Auger electron spectroscopy (XAES) and temperature-programmed reduction (TPR). Analysis of Pd XPS/XAES spectra reveals that palladium is present on the gamma -alumina support in the metallic form. Copper is reduced at lower temperatures in the presence of palladium particles compared to the CuO/gamma -Al2O3 sample. Due to the low copper content in catalysts (sigma (Cu)approximate to 10(14) atoms cm(-2)), the XPS/XEAS spectral features of reduced copper species are quite different from those of bulk copper. As shown by TPR and XPS/XAES data, formation of highly dispersed Pd-Cu bimetallic clusters is suggested. It was discovered by means of TPR analysis that the catalyst preparation in which the gamma -alumina support is impregnated first by copper salt, results in higher formation of the Pd-Cu alloy. (C) 2001 Elsevier Science B.V. All rights reserved.