DISPERSION AND REACTIVITY OF MOLYBDENA ON THE SURFACE OF ALUMINA

Several series of molybdenum oxide catalysts supported on gamma-Al2O3 prepared by a mechanical mixture of both oxides have been studied by X-ray diffraction and Laser Raman spectroscopy. The formation of bulk molybdena is observed after monolayer coverage has been reached (0.71 theoretical monolayers). Calcination at 770K in wet oxygen favours the dispersion of molybdenum species leading to polymolybdate formation, while under dry oxygen a lower degree of dispersion is achieved, and the polymolybdate species are not formed. The formation of molybdenum species on the gamma-Al2O3 surface is also studied as a function of calcination time.