Thermal Decomposition of Ammonium Paratungstate Tetrahydrate Traced by In Situ UV/Vis Diffuse Reflectance Spectroscopy



In situ UV/Vis diffuse reflectance spectra of ammonium paratungstate tetrahydrate at increasing temperatures were recorded in oxidative as well as in reductive atmospheres. From the edge energy of the ligand-to-metal charge transfer transition of tungsten ions, the number of bridging W–O–W bonds, N, was determined. The increase of N with temperature indicates a stepwise enhancement of the condensation of WO6 octahedra to finally form WO3 in an oxidative atmosphere.