STUDY BY TEMPERATURE PROGRAMMED REDUCTION (TPR) OF THE PURE AND SILICA-SUPPORTED HNXW12O40 HETEROPOLYACIDS (X = P, SI)

The H(n)XW12O40(X = P, Si) heteropolyacids were studied by Temperature Programmed Reduction (TPR), The pure compounds show two peaks corresponding to the reduction of WO3 into WO2.72 and WO2.00. The TPR curves of the supported heteropolyacids are more complex and show, that there are two polyanionic species on the support. The first compound is bulk polyacid which crystallized near or on the silica surface while the second one is polyanion in interaction with silica. Depending on the polyanion, this late species is more or less reducible than the pure compound.