Electrostatic Self-assembly of Polyoxometalates on Chitosan as Catalysts of Oxidation of Cyclic Hydrocarbons

The Keggin type heteropolyacids of tungsten and molybdenum (HPW and HPMo) and heteropolyacid salts of cobalt with changing stoichiometry H₃-₂x Co x PM₁₂O₄₀ where M = Mo or W, x = [fraction one-half], 1, 1[fraction one-half] were synthesized and immobilized on chitosan. The complexes were characterized by X-ray diffraction and for first time by zeta potential measurements. These complexes were employed as catalysts in the cyclooctane oxidation with molecular oxygen. The introduction of cobalt into HPW structure shows a substantial influence on the catalytic activity of heteropolyacid salts in the oxidation of cyclooctane while the incorporation of cobalt atoms into HPMo only to some extent improves its catalytic properties. The cobalt molybdophosphates supported on chitosan show a similar catalytic activity as unsupported catalysts while the catalytic activity of cobalt tungstophosphate upon immobilization decreases.