Catalytic oxidation of 1-butene over bismuth molybdate catalysts : IV. Dependence of activity on the structures of the catalysts

A new method to prep. Bi2O3-MoO3 catalysts consisting in boiling slurries of mixts. of freshly prepd. and thoroughly washed Bi(OH)3 and molybdic acid has been developed. Catalysts prepd. in this way are more active, more selective, and better reproducible than those obtained by other methods. These catalysts were investigated after various heat treatments by room-temp. x-ray anal., in K Br wafer techniques, and reflection spectroscopy. Moreover, their activities were detd. for the 1-butene oxidative dehydrogenation. Superior catalytic activity appears confined to the compds. Bi2O3.MoO3 (the low-temp. koechlinite modification) and Bi2O3.2MoO3. This activity is connected to the presence of corner sharing Mo-O octahedra in the bulk of the solid, that give rise to tegragonal pyramidal Mo-O sites at the surface also sharing only corners with neighbors. The promoting influence of Bi2O3 then might also arise because of forcing this structure on the MoO3 component.