Abstract: The oxidition-reduction behaviour of Keggin and Dawson types of molyb dophosphoric heteropolyacids and molybdovanadophosphoric heteropol yacids was studied by cyclic voltammetry in the mixed solvent of water-dioxane containing supporting electrolyte, 0.1 mol/L H₂SO₄.　The ability and reversibility of the oxidation-reduction of molybdenum and vanadium were analyzed. The influence of vanadium content on the oxidation-reduction beha viour of the molybdovanadophosphoric heteropolyacids was also discussed. The abi lity of the oxidation-reduction of Dawson type of the molybdophosphoric heteropo lyacids is stronger than that of Keggin type of the molybdophosphoric acids. The reversibilities of the oxidation-reduction of molybdenum and va nadium became worse both for the Keggin and Dawson types of the molybdovanado phosphoric heteropolyacids with the increase of vanadium content. The characteri stic fingerprint of these compounds allows us to distinguish the Dawson type mol ybdophosporic heteropolyacids from the molybdovanadophosphoric heteropolyacids.

Key words: molybdophosphoric heteropolyacid, molybdovanadophosphoric heteropolyac id, redox reaction, cyclic voltammetry