This invention relates to a method of preparing oxides of W, Mo or mixed metal oxides thereof. More particularly, a reduced metal oxide containing an ammonium or substituted ammonium cation is treated with aqueous hydrogen peroxide, followed by heat treatment in an oxygen containing atmosphere.
Tungsten and molybdenum bronzes are known in the art. These bronzes contain metal cations and have different structures such as pervoskite, tetragonal, intergrowth and hexagonal. Bronzes having a hexagonal structure are of particular interest due to the formation of hexagonal tunnels. It has been presumed that the metal cations occupy the tunnel sites thus imparting stability to the overall structure. Hexagonal ammonium tungsten bronzes are described in Trans. Faraday Soc., 67, 794 (1971). These compounds are prepared by reducing ammonium paratungstate in a hydrogen atmosphere. The structures of alkali metal hexagonal tungsten bronzes which are prepared by heating alkali tungstate, tungsten dioxide and tungsten trioxide in vacuo are reported in Mat. Res. Bull., 14, 667 (1979). According to Inorg. Chem., 5, 1559 (1966), a rubidium molybdenum bronze having a hexagonal structure was prepared by heating Rb.sub.2 MoO.sub.4, MoO.sub.3 and Mo at high temperatures.
In 1961, it was discovered that a hexagonal tungsten bronze structure could be obtained with vacant tunnel sites in mixed molybdenum-tungsten oxide compounds wherein Mo atoms replaced some W atoms in the oxide framework (Acta. Cryst., 14, 379 (1961)). A recent series of papers reports the synthesis and properties of pure hexagonal WO.sub.3 with vacant tunnel sites, 9th Int. Cong. on Electron Microscopy, 1, 260, (Toronto, 1978); J. Solid State Chem., 29, 429 (1979); 9th Int. Symp. Reactivity of Solids, VI-18, 660 (Cracow, 1980). The reported synthesis is represented schematically as ##STR1##