Microstructure and catalytic performances of chitosan intercalated montmorillonite supported palladium (0) and copper (II) catalysts for Sonogashira reactions.

In this study, an efficient heterogeneous catalytic material including Pd nanoparticles and Cu cations supported on montmorillonite/chitosan (MMT/CS) composite was prepared by solution intercalation and complexion methods. The valence states of Pd (both Pd(0) and Pd(II) coexisting) and Cu (mainly Cu(II)) of the Pd/Cu@MMT/CS catalyst were confirmed by the X-ray photoelectron spectroscopy (XPS) characterization. The d spacing was enlarged from 1.25nm (MMT) to 1.94nm (Pd/Cu@MMT/CS). Pd/Cu@MMT/CS catalyst had obviously bigger specific surface area (S) and total pore volume (V) than pure MMT. High resolution transmission electron microscopy (HR-TEM) observation of the Pd/Cu@MMT/CS catalyst showed that separated Pd nanoparticles sized below 3nm dispersed well both in the interlayer space and surface of MMT layers. The positron annihilation lifetime spectroscopy (PALS) was very sensitive to the microstructure changes caused by the formation of nano particles Pd after reduction of Pd/Cu@MMT/CS to Pd/Cu@MMT/CS. The prepared Pd/Cu@MMT/CS catalysts are highly active for the Sonogashira reactions of aromatic halides and alkynes in HO/ether solution, and can be recycled 6 times. The leaching of Cu species is much quicker than Pd species during recycling, which should be the main reason for the decrease in efficiency of the recycled Pd/Cu@MMT/CS catalysts.