CO2-promoted water-medium Ullmann reaction over a Pd/phenyl-SBA-15 mesoporous catalyst

Water-medium Ullmann reaction was carried out in CO2 atmosphere over the mesoporous Pd/Ph-SBA-15 catalyst exhibiting high activity and selectivity owing to the uniform dispersion of Pd particles and hydrophobilic mesoporous channels which facilitate the diffusion and adsorption of organic molecules, especially in an aqueous medium. The CO2 also shows promoting effect on activity and selectivity, which could be understood by considering the role of H+ in the mechanism of Ullmann reaction. The optimum Ph-Ph yield (84.0%) was obtained at PCO2 = 0.8 MPa and V-H2O =6.0 mL and could remain almost unchanged even after the catalyst has been used repetitively for 5 times.