The effect of potassium in the preparation of magnesium orthovanadate and pyrovanadate on the oxidative dehydrogenation of propane and butane

The catalytic properties of magnesium orthovanadate, magnesium pyrovanadate, and mixed oxides of vanadium and magnesium in the oxidative dehydrogenation of propane and butane were studied. The mixed oxides prepared by two different methods, with or without the use of K, were compared. For samples without K, Mg orthovanadate was quite selective for the oxidative dehydrogenation of both propane and butane, whereas Mg pyrovanadate was selective only for propane. However, samples that contained residual K showed decreased selectivity. The mixed oxides were selective for both hydrocarbons, although those prepared without K contained only orthovanadate as the vanadate phase, whereas those prepared with K contained both orthovanadate and pyrovanadate phases. However, judging from the CO/CO₂ ratios, all mixed oxides behaved as if they contained only Mg orthovanadate on the surface. Upon heating the samples, the concentration of potassium on the surface increased. Finally, interesting correlations between the rates of consumption of oxygen and of different alkanes were observed.