Solid-State Chemistry of Supported Metal Oxides

3 Solid-State Chemistry of Supported Metal Oxides. The ability to discriminate between the multiple states present in supported metal oxides with Raman spectroscopy provides a convenient probe to monitor the structural transformations that occur in such systems with increasing temperature. The transformations that occur for 10% WO3 supported on AI2O3 as the calcination temperature is increased is shown in the Raman 

More detailed studies demonstrate that crystalline Al2(W04)3 is produced from the direct solid-state reaction between crystalline WO3 and the alumina support and occurs by the migration of alumina to the WO3 particles at these elevated temperatures. The initial transformation of the surface tungsten-oxide phase to crystalline WO3 particles at elevated temperatures, when the alumina surface area decreases, reveals that the tungsten-oxide species are not miscible in the alumina support and are actually diffusing away from the alumina support. Thus, it appears that the surface tungsten oxide-alumina mixed oxide forms an immiscible oxide system because of the inability of the alumina support to accommodate the large charge and size of the cation. More recent Raman studies 

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