Study of the Co-VPO interaction in promoted n-butane oxidation catalysts Original Research Article

Cobalt-impregnated VPO catalysts were prepared using different cobalt salts and impregnation methods. The catalytic tests showed that cobalt impregnation significantly increased the overall activity. The use of cobalt acetyl acetonate led to a more selective high loading catalyst. To investigate the origin of the cobalt effect, the solids were characterized using XRD, Raman spectroscopy, FT-IR, and XPS. The surface acidity was probed by adsorbing acetonitrile. No structural effects were detected through XRD. After 700 h on stream, the only phase detected in all cases was V(IV) vanadyl pyrophosphate. The surface oxidation state of vanadium was V(IV). The Co 2p XP spectrum showed an intense shoulder at 788 eV, indicating that Co(II) species were present. The concentration of very strong Lewis acid sites increased at higher cobalt loading, but its strength was unaffected.