An investigation of the titanium–antimony–oxygen system by X-ray diffraction, antimony-121 Mössbauer spectroscopy, and temperature-programmed reduction
Titanium–antimony oxides have been prepared by precipitation methods and investigated by a number of techniques. Powder X-ray diffraction has shown the initial precipitates to be amorphous materials which begin to form distinguishable crystalline phases when calcined in air at temperatures exceeding ca. 500 °C. The nature of the crystalline phases depends on the relative concentration of the titanium and antimony cations in the initial precipitates and the calcination temperatures. The oxidation states of antimony in the materials have been determined by antimony-121 Mössbauer spectroscopy. The materials formed at temperatures exceeding 1 000 °C may be described as solid solutions of < ca. 4% antimony(V) in titanium(IV) oxide. The reducibility of some amorphous hydroxides and crystalline oxides of titanium and antimony when treated in hydrogen and the nature of the reduction products has been studied by temperature-programmed reduction and antimony-121 Mössbauer spectroscopy. The results demonstrate the complementary nature of the two techniques and their capacity to examine the character of reduction processes in the amorphous and crystalline solid state. Similar investigations of the titanium–antimony oxides showed that the reduction properties of the materials in hydrogen are sensitive to the precalcination history and antimony concentration. Low concentrations of antimony in the mixed oxide phases dried in air at low temperatures suffered facile reduction in hydrogen at moderate temperatures, whereas similar concentrations of antimony(V) in titanium dioxide formed by high-temperature calcination were particularly stable to reduction in hydrogen.