Co-immobilization of Pd and Zn nanoparticles in chitosan/silica membranes for efficient, recyclable catalysts used in ullmann reaction.

In this study, an efficient heterogeneous catalyst including palladium (Pd) and zinc (Zn) nanoparticles supported on chitosan/silica (CS/SiO) composite membrane is synthesized using partially etching of SiO technique. N sorption isotherm results shows that the prepared Pd-Zn@CS/SiO (1/1) porous membrane had a BET surface area of 26.50m/g. High-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS), characterization of the catalyst shows that the Pd nanoparticles (below 5nm), and Zn aggregates (about 10-15nm) dispersed well in the CS/SiO matrix. Zinc crystal was also detected by X-ray diffraction study and HR-TEM observation. The prepared Pd-Zn@CS/SiO membrane catalyst is highly active for Ullmann reductive homocoupling reactions of aryl iodides and aryl bromides, and can be recycled 5 times without significant loss of activities. This work supplies a successful approach to realize Pd catalysts and Zn reducing reagent co-immobilized in the same carrier material with excellent catalytic performances.