Cr/V/Sb mixed oxide catalysts for the ammoxidation of propane to acrylonitrile - Part I: Nature of the V species

Rutile-type Cr/V/Sb mixed oxides, catalysts for the ammoxidation of propane to acrylonitrile, were prepared and characterized. For atomic ratios between components equal to Cr/V/Sb 1/x/1 and 1/x/2 the systems were monophasic, but different types of compounds formed depending on the ratio between the three metals. The compositional parameter which most affected the nature of the compound formed was the (Cr + V)/Sb atomic ratio. When this ratio was between 2 and approximate to1, a rutile Cr3+ /V4+ /Sb5+ mixed oxide of composition Cr-1 VxSb1 O4+2x developed (0 < x < 1), which in practice corresponds to a solid solution between 1 CrSbO4 and x VO2. When the (Cr + V)/Sb ratio was between 0.5 and approximate to1, a rutile Cr3+ /V3+ /Sb3+ /Sb5+ mixed oxide of composition CrVxSb1+x+2zO4+4+4z developed (0 < x < 1), which corresponds to a solid solution between 1 Cr3+Sbz3+Sb1+z5+ and x VSbO4. The distinction between the two classes of compounds was not clear-cut, and when the (Cr + V)/Sb atomic ratio was around 1, mixed oxides containing both V3+ and V4+ formed. Values of the (Cr + V)/Sb atomic ratio lower than approximate to0.5 led to the additional formation of antimony oxide. (C) 2002 Elsevier Science B.V. All rights reserved.