An X-ray photoelectron spectroscopy investigation of a novel Pd-Pt colloid catalyst

A Bi-promoted charcoal-supported Pd-Pt oxidation catalyst prepared from colloidal NOct(4)Cl-stabilized Pd-Pt nanoparticles was investigated by means of X-ray photoelectron spectroscopy (XPS). Pd 3d, Pt 4f, Bi 4f, C 1s and O 1s spectra of the colloid, the supported colloid catalyst and a conventional charcoal-supported Pd-Pt/Bi coimpregnation catalyst (Degussa, CEF 196 RA/W) were measured. Both catalysts were explored unused (as-prepared) and after deactivation in the heterogeneous catalytic oxidation of glucose to gluconic acid. The spectra are analyzed to elucidate the higher starting activity of the Pd-Pt/Bi/C colloid catalyst, especially the role of the promotor Bi and the mechanisms leading to catalyst deactivation. The higher starting activity of the colloid catalyst is explained by the presence of completely reduced Pd and Pt, threevalent Bi and a smaller particle size in contrast to the conventional catalyst which contains partly oxidized Pd and a non-unique chemical state of Bi. The deactivation of both catalysts is suggested to be due to metal dissolution, particle growth and chemical poisoning. (C) 1998 Elsevier Science B.V. All rights reserved.