Enhanced activity of Pd–Cu(Ni) bimetallic catalysts for oxidative carbonylation of phenol

Pd–Cu(Ni) bimetallic catalysts supported on Pb-doped manganese oxide octahedral molecular sieves(Pb-OMS-2) were prepared by deposition-precipitation method, and the activities of those bimetallic catalysts were evaluated in the oxidative carbonylation of phenol to diphenyl carbonate (DPC). The physico-chemical properties of catalysts were evaluated by various characterization techniques such as X-ray diffraction (XRD), Transmission electron microscope (TEM), Scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy (STEM/EDS), Temperature-programmed reduction of hydrogen (H2-TPR) and X-ray photoelectron spectroscopy (XPS). The results showed that superior activity of bimetallic catalyst was accomplished by the addition of second metal Cu(Ni) compared to monometallic Pd catalyst. The metal particles of bimetallic catalysts were dispersed homogeneously on the surface with small particle size (3∼5 nm). The high activity and stability of bimetallic catalyst were achieved due to the formation of very active Pd–Cu(Ni) interfaces. The oxidation state of active species increased via the strong interaction between bimetallic components, and the redox capacity of Pd became stronger with the addition of the second metal. The highest DPC yield was 23.4% for Pd1Cu2 and 22.9% for Pd1Ni4 catalysts, respectively. After 20 h of reaction time, even though the DPC yield stopped growing for the monometallic catalysts, it continued to increase for the bimetallic catalysts, and the DPC yield reached about 50.0% at 24 h.