Effect of the structure of Ti-Sb-O catalysts on their acid-base properties, surface oxygen binding energy, and catalytic properties in propylene ammoxidation

The structure of Ti-Sb-O catalysts, namely, a solid solution of antimony ions in rutile-type TiO 2 and the titanium antimonate TiSb 2 O 6 , is characterized by X-ray diffraction, high-resolution electron microscopy, calorimetry, and IR spectroscopy. The structure effects on the acid-base properties and the surface oxygen binding energy are considered, as well as the correlation of these characteristics with the catalytic properties of the Ti-Sb-O system in propylene ammoxidation. The solid solution has a regular crystal structure. As a consequence, the surface has high concentrations of strong aprotic acid and strong basic sites and is characterized by a high surface oxygen binding energy. In the titanium antimonate structure, extended crystallographic shear defects cause a marked enrichment of the surface with antimony and, accordingly, an increase in the relative concentration of weak aprotic acid sites and a decrease in the surface oxygen binding energy. The changes of the structure and acid-base properties of the surface in passing from the solid solution to TiSb 2 O 6 result in an increase in the acrylonitrile selectivity.