The bulk and surface properties of PdCl2-CuCl2-CH3COOK catalysts supported on activated carbon (a.c.) used in the synthesis of dimethyl carbonate (DMC) by gas-phase oxidative carbonylation of methanol were characterized by XRD and XPS techniques. On the basis of the catalyst characterization and evaluation results, the active species of the catalyst has been suggested, and the reaction mechanism of oxidative carbonylation has been proposed. The interaction between CH3COOK and PdCl2 or CuCl2 on the activated carbon support has been deduced from the formation of KCl, and the partial reduction of CuCl2-CuCl has been found. Furthermore, the presence of CuCl2 inhibits the reduction of PdCl2. The experimental results show that the main reason for catalyst deactivation could be attributed to the loss of chlorine. Fortunately, promoter CH3COOK could inhibit the loss of chlorine, and improve the electronic environment of PdCl2-CuCl2 catalyst, so that the stability and activity of the catalyst PdCl2-CuCl2-CH3COOK/a.c. increase. (C) 2002 Elsevier Science B.V. All rights reserved.