Two series of samples were prepared by the copptn. and the impregnation methods. The surface acidity of these samples was determine The structure, surface concentration of MoO3, and the types of surface acidic sites were measured by XPS, x-ray diffraction, IR, and laser Raman spectroscopy. For these 2 series of samples, the surface structure, the trend of the change of surface acidity, and the surface chem. state of MoO3 remarkably depend on the preparation method. For the samples obtained by copptn., MoO3 exists on the surface in 2 different chem. states which have completely opposite effects on the surface acidity.

Key words: X-RAY DIFFRACTION ANALYSIS, SILICON OXIDE, SURFACE STRUCTURE, SURFACE CHEMISTRY, ACIDITY, MOLYBDENUM OXIDE, COPRECIPITATION, DIPPING, LASER, RAMAN SPECTROMETRY