CHARACTERIZATION OF THE ACTIVE PHASE IN CESIUM-DOPED IRON-VANADIUM-OXIDE CATALYSTS FOR THE SELECTIVE OXIDATION OF POLYAROMATICS

The addition of caesium sulphate to unsupported vanadium-iron-oxide ma terials leads to the formation of an amorphous non-stoichiometric phas e, as well as the crystalline phases, FeVO4, Fe2V4O13, and Fe1-XS (pyr rhotite). Caesium was only present in the amorphous parts of the sampl e, and the amount of the new phase formed was found to vary depending on the vanadium : iron ratio and the amount of caesium dopant added. T he new phase contains Fe3+ ions with oxide lattice vacancies in their coordination sphere, i.e. Fe3+-V-0(e(-)) species. Catalytic testing de monstrated that the caesium-doped samples were more selective for the oxidation of fluorene to 9-fluorenone. The role of the caesium is prob ably to modify the surface acidity of the catalyst and act in the form ation of stable oxide lattice vacancies.