The laser Raman spectra of MoO3/g-Al2O3, MoO3/TiO2, and MoO3/SiO2 were measured. The spectra of MoO3/g-Al2O3 and MoO3/TiO2 were compared with those obtained after adsorption of pyridine and with those after treatment with aqueous NH3 solution The coordination states of Mo in monolayer dispersed MoO3 (i.e., the 2-dimensional polymeric surface Mo species with its typical bond at ~950 cm-1) are not the same. One kind of surface species (Mo-1) cannot adsorb pyridine and is insoluble in aqueous NH3 solution, which means that it is not the acidic site. The other surface species (Mo-2) can adsorb pyridine and is soluble in aqueous NH3 solution, which indicates that this species is closely related with the surface acidity of the catalysis. Mo-1 is probably a tetrahedrally coordinated surface species and Mo-2 is a octahedrally coordinated species. The fraction of Mo-2 in MoO3/SiO2 is larger than that in MoO3/g-Al2O3, and the interaction between MoO3 and SiO2 support is weaker than that in MoO3/g-Al2O3, so that all the MoO3 in MoO3/SiO2 is soluble and the ratio between acidic sites and surface Mo6+ approaches unity.

Key words: ALUMINIUM OXIDE, SILICON OXIDE, SURFACE STRUCTURE, TITANIUM OXIDE, MOLYBDENUM OXIDE, SUPPORTED CATALYST, RAMAN SPECTROMETRY