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

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.