John Ward Jenkins

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 Mossbauer 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 Mossbauer 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.

Reduction of titanium—antimony oxides in hydrogen and in carbon monoxide

Abstract The reduction of coprecipitated titanium-antimony oxides by hydrogen and carbon monoxide has been investigated. The results show that the selective oxidation of hydrogen or carbon monoxide by antimony in titanium-antimony oxides is dependent on the temperature, the nature of the matrix and the extent of catalyst reduction. The oxidation of hydrogen, as compared to carbon monoxide, at moderate temperatures is strongly favoured by solids composed of low concentrations of antimony in the rutile lattice and subjected to limited overall reduction. The results may be associated with the use of such materials as selective hydrocarbon oxidation catalysts.