Anaerobic oxidative dehydrogenation of n-butane over MgVO catalysts

The oxidative dehydrogenation of n-butane under anaerobic conditions was studied using three catalysts prepared based on a mixture of vanadium with magnesium oxides, one without a support (B16) and two supported over a 30 wt % of a third oxide, SiO₂ (S16) or α-Al₂O₃ (A16). The n-butane conversion and the selectivity toward butadiene decreased as the time on run increased. The reaction rate control gradually changed from chemical to the diffusion of oxygen through the catalyst structure as the time on run increased, with a selectivity always higher than in aerobic conditions. Supported catalysts were more active than the non-supported one. After reoxidation, the catalysts recovered the original activity and selectivity without any damage to the visible structure. During the reduction cycle, a decrease in the amount of V⁵⁺ with the simultaneous appearance of increasing amounts of V⁴⁺. The presence of a lower oxidation state was never found and after reoxidation, the only species present was V⁵⁺. This is an abstract of a paper presented at the 8th World Congress of Chemical Engineering (Montréal, Quebec, Canada 8/23-27/2009).