Multifunctional mesoporous silica supported palladium nanoparticles as efficient and reusable catalyst for water-medium Ullmann reaction

Multifunctional mesoporous material (NH2&Ph-SBA-15) was synthesized by co-condensation of tetraethyl orthosilicate, amine-silane and phenyl-silane in the presence of triblock copolymer P123. The Pd nanoparticles immobilized on the NH2&Ph-SBA-15 support were fabricated by the impregnation and subsequent reduction method. The XRD, TEM, N-2 sorption, IR and solid NMR measurements revealed that this novel mesoporous Pd catalyst (Pd/NH2&Ph-SBA-15) not only maintained ordered hexagonal mesopores, but also possessed characteristics of the two organic functional groups on the mesopore surface. Compared with Pd nanoparticles supported on the parent SBA-15 or monofunctionalized mesoporous materials, it displayed much higher catalytic reactivity and selectivity in the water-medium Ullmann reaction. This could be attributed to the synergic promoting effect derived from binary organic functional groups since the NH2-groups led to the uniform dispersion of Pd nanoparticles inside the pore channels while the Ph-groups decreased the diffusion limitation of organic molecules in water. Furthermore, it could be conveniently recovered and recycled six times without significant loss of activity and selectivity.