EFFECT OF STEAM ON THE OXIDATIVE DEHYDROGENATION OF BUTENE OVER MAGNESIUM FERRITES WITH AND WITHOUT CHROMIUM SUBSTITUTION

Single-phase spinel magnesium ferrites with and without chromium substitution were studied in the oxidative dehydrogenation of butene to butadiene. MgFe2O4 exhibits a low turn-over temperature, of but-1-ene to butadiene and a selectivity independent of the O2-to-C4 ratio. The catalytic properties of ferrites can be well correlated with their crystallographic structures. Having a structure of inverse spinel, MgFe2O4 exhibits catalytic features similar to that of gamma-Fe2O3, another inverse spinel catalyst, but different from that of ZnFe2O4, a normal spinel ferrite. The chromium substitution has little effect on the performance of magnesium ferrite in the presence of sufficient gaseous oxygen. The effect of steam is, however, strong. Significant increases in both the activity and the selectivity to butadiene were observed upon the introduction of steam to the reactor. This promotion effect of steam is attributed to the hydroxylation of the catalyst surface.