Preparation of reduced molybdenum oxides (MoO₂MoO₃) by a sol-gel method

Molybdenum oxides were prepared by a sol-gel method using molybdenum chloro-ethoxide as a precursor. MoCl₅, ethanol and potassium metal were used as starting materials. KCl by-product was filtered out. All reactions proceeded in methane dichloride solvent at room temperature. Blue amorphous precipitates which look like "molybdenum blue" were obtained after evaporation of solvent. This product crystallized to MoO₃ on heating to 300 °C in air, to MoO₂ on heating in vacuum and to Mo₄O₁₁ together with MoO₃ and MoO₂ when heated in He gas. The valence of molybdenum in the blue, as-prepared sample, ranges from 4 to 6 and could not be determined unambiguoulsy by IR and XPS spectra. The molybdenum oxide products incorporated 25-35 wt% of physically adsorbed solvent and/or reaction product (H₂O, C₂H₅OH) and retained ethoxy and hydroxyl groups; the adsorbed species and retained ethoxy groups are lost on heating at ∼200 °C and at ∼400 °C, respectively. About 1-6 wt% of chlorine was also retained in the product, most of which was removed on heating to 160 °C in air.