Bismuth molybdates: Preparation and catalysis

Abstract Only one bismuth molybdate, Bi 2 MoO 6 or the Koechlinite phase, has proved to be an active catalyst for olefin oxidation. The activities of the other compounds, Bi 2 Mo 2 O 9 and Bi 2 Mo 3 O 12 are merely due to coverage of these compounds by Bi 2 MoO 6 . This coverage is also due to the fact that the Koechlinite phase is quickly obtained from the reactants, whereas the other compounds are obtained more slowly. Koechlinite is active and stable, but sensitive to decomposition if not treated properly. A procedure is described for obtaining pure and active Koechlinite crystals. Such a procedure is important, because the natural mineral Koechlinite is always contaminated with quartz. Surface models are given to explain the selectivity, the non‐selective reaction, oxygen diffusion and deactivation of differently prepared bismuth molybdate catalysts.