A structural study of tin-antimony oxide catalysts by high-resolution electron microscopy

Tin-antimony oxide catalysts prepared by the calcination of precipitates have been investigated by high-resolution electron microscopy. The exposure of the catalysts prepared at low temperatures to gaseous atmospheres containing hydrocabon and oxygen results in a segregation of antimony from the poorly crystalline rutile-type solids and the development of an amorphous material. The catalysts containing low concentrations of antimony are also partially converted to a non-rutile-type crystalline phase. Prolonged calcination in air of the used catalysts at high temperatures leads to the attainment of bulk equilibrium and the formation of solid solutions of antimony in tin(IV) oxide. Treatment of the equilibrated crystalline catalysts prepared at high temperatures in the hydrocarbon and oxygen gas stream gives rise to disorder within the catalyst structure which is resistant to further change at high temperatures.