Silica-included heteropoly compounds as solid acid catalysts

12-Tungstophosphoric acid (H3PW12O40) and its acidic cesium salt (Cs2.5H0.5PW12O40), which readily dissolve or disperse as a colloid in water or in highly polar organic media, could be immobilized into a silica matrix by means of a sol-gel technique. This involves the hydrolysis of ethyl orthosilicate to afford insoluble and easily separable solid acid catalysts. The silica-included heteropoly compounds thus obtained were porous materials with mesopores and large surface areas, and were thermally more stable than the acidic ion-exchange resin Amberlyst-15. They effectively catalyzed the hydrolysis of ethyl acetate in the liquid phase owing to their strong acidity. Their turnover frequencies were larger than those of Amberlyst-15 and H-ZSM-5. H3PW12O40, when included in a silica matrix, showed higher catalytic activity than as an aqueous solution.