The oxidation state of Ge on Pd/C catalysts investigated by XPS

A commercially available 15%-Pd-on-active-carbon catalyst was modified with a Ge sub-monolayer to make it suitable for hydrogenation reactions. Two mo dified catalysts were prepared via reductive adsorption of Ge4+, the Ge con centrations on the Pd surface being equivalent to 0.18 and 0.71 monolayer, respectively. Information about the valence state of the Ge on the Pd/C catalysts for fre sh and hydrogen-treated samples was obtained using X-ray photoelectron spec troscopy (XPS) and X-ray induced Auger electron spectroscopy (AES). The hyd rogen-treated catalyst samples were handled in a high-quality glove box dir ectly coupled to the XPS instrument, to prevent re-oxidation of the samples . The high resolution XPS results, as well as the position of the Auger line, the line shape of the Auger line and the Auger parameter, all show that th e Ge present in sub-monolayer concentration on the freshly prepared Pd cata lyst is present in oxidised form and that it can be reduced completely to t he metallic state in a H-2 atmosphere at low (50 degrees C) temperature. (C ) 1999 Elsevier Science B.V. All rights reserved.