An investigation of carbon-supported CuCl2/PdCl2 catalysts for diethyl carbonate synthesis

The synthesis of diethyl carbonate (DEC) by the oxidative carbonylation of ethanol was investigated using catalysts prepared by the dispersion of CuCl2 and PdCl2 on amorphous carbon promoted with KCl and NaOH. Catalysts were characterized extensively by XRD, XAFS, SEM and TEM with the aim of establishing their composition and structure after preparation, pretreatment, and use. It was observed that after preparation and pretreatment in He at 423 K copper is present almost exclusively as Cu(I), most likely in the form of [CuCl2](-) anions, whereas palladium is present as large PdCl2 particles. Catalysts prepared exclusively with copper or palladium chloride are inactive for DEC synthesis, indicating that both components must be present together. Evidence from XANES and EXAFS suggests that the DEC synthesis may occur on [PdCl2-x][CuCl2](x) species deposited on the surface of the PdCl2 particles. As prepared catalysts exhibit an increase in DEC synthesis activity and selectivity with time on stream, but then reach a maximum activity and selectivity, followed by a slow decrease in DEC activity. The loss of DEC activity is accompanied by a loss in Cl from the catalyst and the appearance of paratacamite. (C) 2009 Elsevier B.V. All rights reserved.