Synthesis of dimethyl carbonate from methanol and carbon dioxide in the presence of polyoxometalates under mild conditions

Zirconia supported Keggin unit, 12-tungstophosphoric acid/zirconia (H3PW12O40/ZrO2), was prepared via sol-gel technique. As-synthesized composites were characterized by ICP-AES, IR spectroscopy, nitrogen adsorption determination, X-ray diffraction (XRD), and P-31 magic-angle spinning NMR spectroscopy (MAS NMR), indicating that the primary Keggin structure remained intact after formation of the composites, and that the composites contained both Bronsted and Lewis acid sites. Selective synthesis of dimethyl carbonate (DMC) from methanol and CO2 was investigated in the presence of H3PW12O40/ZrO2 catalysts under mild conditions. The effects such as the amount of catalysts, reaction temperature and CO2 pressure on the DMC formation were studied, indicting that the catalytic activity depend strongly on the CO2 pressure. When the reaction was carried out at various pressure of CO2, two maxima in DMC synthesis were observed at 4 and 7.6 MPa, and the byproducts such as dimethyl ether and CO were hardly detected. Bronsted acid sites in the H3PW12O40/ZrO2 composites can devote to methanol activation and to the enhancement of the catalytic activity of ZrO2 support. (C) 2003 Elsevier B.V. All rights reserved.