A LASER RAMAN-SPECTROSCOPY STUDY OF MOLYBDENUM OXIDE-SUPPORTED ON ALUMINA AND TITANIA

Molybdenum oxide supported on alumina and titania prepared by three di fferent methods (impregnation, calcination and hydrothermal treatment of mechanical mixtures), have been studied by laser Raman spectroscopy . Different oxomolybdenum species have been detected depending on the method of preparation and on the calcination conditions. Heptamolybdat e and polymolybdate species were found in the impregnated and in the u ncalcined, hydrothermally treated samples supported on alumina and tit ania, respectively, whereas polymolybdate species were formed on the s urface of alumina when the mechanical mixtures and the hydrothermally treated samples were calcined in the presence of water vapour. However , two kinds of species, polymolybdate and mono-oxomolybdenum, were fou nd in the case of the mechanical mixtures and the hydrothermally treat ed samples calcined in the presence of water vapour when supported on titania.