Influence of the bulk and surface properties on the performance of iron–antimony catalysts

Abstract

The modifications induced in Fe–Sb catalysts by the introduction of an excess of antimony oxide, which is needed in order to obtain highly selective catalysts in the ammoxidation of propylene to acrylonitrile, were investigated by means of X-ray diffraction (X.r.d.), X-ray photoelectron spectroscopy (X.p.s.) and Mössbauer spectroscopy.

More important than increasing the surface Sb: Fe ratio, a promoting effect by an excess of Sb was found to develop during activation through the formation of structurally distorted and defective FeSbO₄, which appears to be the active phase. Fe²⁺ ions are thus introduced into the iron antimonate rutile structure near oxygen vacancies. These vacancies are possibly connected with the adsorption sites for the more strongly bound oxygen species that is responsible for allylic oxidation.