Effect of the promoter copper on the oxidative carbonylation of phenol to diphenyl carbonate (DPC) over the ultrafine embedded catalyst Pd-Cu-O/SiO2, was studied. The promoter copper is divided into the heterogeneous Cu(II) contained in the catalyst and the homogeneous Cu2+ charged into the reactor directly. The heterogeneous Cu(II) promoter reacts with PdO to form CuPdO2, changing the chemical environment of Pd atoms. This enables the deactivated Pd(0) atoms to easily transfer electrons to the Cu(II) atoms in the crystal lattice of CuPdO2 to be reactivated. However, excess Cu(II) hinders the reactants from contacting the active centers, producing negative effects on the yield of DPC. The homogeneous Cu2+ can promote the change from Pd(0) to Pd(II) more effectively than the heterogeneous Cu(II) because all the Cu2+ in the system can work. However, only the Cu(II) incorporated into the crystal lattice of PdO to form the CuPdO2 can obtain electrons from Pd(0). (c) 2005 Elsevier B.V. All rights reserved.