Synthesis of biphenyl through the C-H bond activation in benzene over a Pd catalyst supported on graphene oxide
This seems a first report on the Carbon-Hydrogen (C-H) bond activation in benzene over a Palladium catalyst supported on graphene oxide (GO) leading to the formation of solely biphenyl with the yield of 78%. The reaction was performed for 12 h in the presence of acetic acid and oxygen at 80 °C. An XPS study indicated that in the initial catalyst Pd is mainly present as Pd(II) species on the GO surface. The interaction of these species with acetic acid during the reaction generates Pd acetate species. A density functional energy (DFT) study revealed that the adsorption of the first benzene molecule on the Pd acetate is weak (0.15 eV) and the energy barrier of the following C-H bond scission is high and equal to 1.67 eV. The adsorption of the second benzene molecule is relatively strong (0.40 eV), the acetic acid molecules release leaving the biphenyl Pd intermediate which gives further the biphenyl molecule formation. The presence of oxygen and acetic acid is needed for closing the catalytic cycle by regeneration of the reactive Pd acetate.