Antimony-121 Mössbauer investigations of tin–antimony oxides

Abstract

Catalytically active tin–antimony oxides have been investigated by ¹²¹Sb Mössbauer spectroscopy. Materials prepared by coprecipitation and dehydrated at 600 °C for 16 h give single-phased blue solids containing both Sb^III and Sb^V in oxygen environments. Materials containing more than 20% antimony and heated for longer periods or at higher temperatures give the segregation of an additional antimony oxide phase. Samples with an antimony concentration of less than ca. 10% contain Sb^V within the tin(IV) oxide rutile lattice. Although the Mössbauer spectra provide evidence for an increase in s-electron density at both tin and antimony nuclei, the data give no indication of any reduction processes leading to the formation of either Sn^II or Sb^III. A mechanism for charge compensation is proposed which involves the delocalization of electrons into a conduction band. The reaction of the tin–antimony oxides with hydrogen and the use of the material in the catalytic oxidation of olefins is accompanied by the reduction of Sb^V to Sb^III.