Effects of inorganic cocatalysts and initial states of Pd on the oxidative carbonylation of phenols over heterogeneous Pd/C

Effects of various metal complexes of Ce, Co, Mn, and Cu compounds and of initial states of Pd with different particle sizes were investigated on coupled oxidative carbonylations of bisphenol-A (BPA) and phenol over activated carbon-supported metallic palladium (Pd/C). In the presence of Ce(CH3COO)3 as the cocatalyst, homogeneous Pd(CH3COO)2 showed a better activity than Pd/C as the main catalyst. From screening of the various inorganic cocatalysts, Cu2O was chosen as the best partner with the activated carbon-supported metallic palladium. More interestingly, this heterogeneous Pd/C-Cu2O catalyst system was superior to the homogeneous catalyst systems such as Pd(CH3COO)2-Ce(CH3COO)3 or Pd(CH3COO)2-Cu2O because it provided increased conversions of bisphenol-A and selectivities to desired para-position carbonylated products. The active phase of palladium in this catalyst system appeared to be metallic Pd, as evidenced by a stronger metallic character of palladium observed after the reaction with X-ray absorption of near edge structure (XANES) of Pd K-edge. In the presence of Pd/C, the nature of metal and ligand of the inorganic cocatalyst significantly affected the catalytic activity and selectivity. However, the initial state of supported Pd showed a negligible effect, even though the metallic character of Pd varied drastically due to increasing Pd loadings or reduction temperatures. [Copyright &y& Elsevier]