Effects of Pb dopant on structure and activity of Pd/K-OMS-2 catalysts for heterogeneous oxidative carbonylation of phenol

Palladium catalysts supported on Pb-cation-doped manganese oxide octahedral molecular sieves were prepared and used for heterogeneous oxidative carbonylation of phenol to diphenyl carbonate in the absence of homogeneous cocatalysts. The synthesized catalysts were characterized by ICP-AES, XRD and XPS techniques. The experimental results demonstrated that an enhanced activity was obtained when Pb2+ entered into the tunnels of cryptomelane by replacing K+ to form a new hollandite-type phase of Pb2−xMn8O16. The promotion effect of Pb dopant on activity was ascribed to the increase of low-valence Mn3+ and OH group, which was favor of reoxidation of Pd0 to active Pd2+ species.