Water-medium Ullmann reaction over a highly active and selective Pd/Ph-SBA-15 catalyst

Abstract

A series of Pd/Ph-SBA-15 catalysts with ordered mesoporous structure are designed by using the phenyl-functionalized SBA-15 (Ph-SBA-15) as supports. These catalysts exhibit higher activity and selectivity toward biphenyl than Pd/SiO₂, Pd/MCM-41, Pd/Ph-MCM-41 and Pd/SBA-15 in a water-medium iodobenzene Ullmann coupling reaction. The promoting effects on the activity and selectivity could be mainly attributed to the high dispersion of Pd active sites, the ordered mesoporous channels and the strong surface hydrophobocity which facilitate the diffusion and/or adsorption of organic reactant molecules, especially in aqueous media. Meanwhile, the relatively large pore channels are favorable for the coupling of iodobenzene to form biphenyl, which is much bigger than the byproduct benzene resulting from the dehalogenation of iodobenzene. The Pd/Ph-SBA-15 catalyst could be separated easily from reaction products and used repetitively several times, showing the superiority over the homogeneous catalysts for industrial applications.