A series of Pd-Au/SiO2 catalysts was prepared by incipient wetness coimpregnation of silica with respective chloride solutions, followed by calcination in air and reduction in hydrogen at 380 degrees C for 15 h. A variety of techniques, chemisorption of hydrogen and carbon monoxide, temperature-programmed reduction, X-ray diffraction, X-ray photoelectron spectroscopy, and neopentane conversion as a catalytic probe, were employed to characterize metal dispersion and interaction between two metal components and the support. It has been discovered that the prepared materials are not uniform : a palladium-rich phase of very high metal dispersion (particle size similar to 1.3 nm) coexists with much less dispersed gold-rich phase (particle size similar to 15 nm). X-ray photoelectron spectroscopy revealed some presence of Si-

Keywords:SILICA-SUPPORTED PALLADIUM;METAL-CATALYSTS;ALLOYS;NEOPENTANE;HYDROGEN;PD/SIO2;PD;CONVERSION;PARTICLES;CO