RELATIONSHIP BETWEEN STRUCTURE AND POINT OF ZERO SURFACE-CHARGE FOR MOLYBDENUM AND TUNGSTEN-OXIDES SUPPORTED ON ALUMINA

Laser Raman spectroscopy was used to characterize alumina-supported molybdenum and tungsten oxides at loadings ranging from 0.5 to 15 wt% Mo and 0.5 to 30 wt% W. The structure of calcined Mo6+/Al2O3 and W6+/Al2O3 was governed by the point of zero surface charge of each system, with the point of zero surface charge being dependent on metal loading. The structures formed by the molybdenum and tungsten overlayers at the sample point of zero surface charge were found to be analogous to the structures formed by molybdenum and tungsten oxyanions in aqueous solution at a solution pH equal to the sample point of zero surface charge.