The decomposition of dimethyl carbonate over copper zeolite catalysts

Direct synthesis of dimethyl carbonate offers prospects for a "green chemistry" replacement to eliminate use of phosgene for polymer production and other processes. Dimethyl carbonate (DMC) production over copper zeolite catalysts has shown high selectivity, however the rate of DMC decomposition becomes significant as the product concentration in the reactor increases, thus limiting the yield of DMC. DNIC decomposition occurs over the residual Bronsted sites of the copper zeolite catalyst, which are present as a result of incomplete copper exchange. Several strategies were investigated to block acid sites during reaction or remove them during catalyst preparation. Pyridine adsorption on acid sites decreased the rate of DNIC decomposition. Aqueous-phase exchange of Li+ ions with ammonium or acid zeolites prior to copper loading greatly decreased residual acidity of the catalyst, resulting in a greatly reduced rate of DMC decomposition. Aqueous-phase exchange of Li+ ions after copper loading reduced the rate of decomposition by 30% without affecting copper performance or copper loading, resulting in higher observed activity of DMC production compared to the conventional Cu+Y catalyst. (C) 2004 Published by Elsevier B.V.