Abstract
The role of oxygen species in the product distribution of oxidative carbonylation of phenol was investigated using metal doped cryptomelane-type manganese oxide octahedral molecular sieves M-OMS-2 (M = Pb, Cr, Ce, Zn) as catalysts supports. The oxygen species of Pd/M-OMS-2 catalysts were characterized by H2-TPR and X-ray photoelectron spectra techniques. The results show that the Pd/Pb-OMS-2 catalyst calcined at 300 °C exhibits lower onset reduction temperature and more active OH− groups compared with the other catalysts, so the best diphenyl carbonate (DPC) yield is obtained. When Pb-OMS-2 was used as a support, a vast majority of by-product was 4-bromophenol, and a small amount of 3-phenoxyphenol and biphenyldiol yielded. However, for the Pd/Cr-OMS-2, Pd/Ce-OMS-2 and Pd/Zn-OMS-2 catalysts, the decreased amount of 4-bromophenol was observed while 3-phenoxyphenol and biphenyldiol yielded remarkably. It is deduced that active OH− groups not only improve the DPC yield, but also promote the formation of 4-bromophenol and deep oxidation of phenol.
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