An XPS, TEM, and TPD study of the oxidation and ammoxidation of propene using mixed Fe-Sb oxide catalysis

Two mixed Fe-Sb oxide catalysts were investigated for the selective oxidation of propene to acrolein and the ammoxidation of propene in the presence of ammonia to acrylonitrile, The techniques used were chiefly X-ray photoelectron spectroscopy (XPS), temperature deprogrammed desorption (TPD), X-ray diffraction, and transmission electron microscopy. After propene dosing TPD experiments were carried out in the absence of gas phase oxygen utilising lattice oxygen for oxidation. The samples contained a 1:1 and 2:1 atomic ratio of Sb:Fe (referred to as SbFe and Sb2Fe, respectively). XPS data indicate that the surface has an antimony oxide enriched selvedge which favours the selective ammoxidation of propene. The Sb enriched surface of SbFe was found to be highly reducible in low pressures of ammonia, yielding a metallic antimony overlayer, Subsequent thermal desorption of this metal coating revealed a surface with an increased iron (III) oxide content which was not so easily reduced and found to be of a lower selectivity to partial ammoxidation products, The Sb2Fe sample was more stable towards reduction. (C) 1996 Academic Press, Inc.