Carbonization of Chitosan in Palladium-Chitosan/ Montmorillonite Composites to Prepare Novel Heterogeneous Catalysts for Heck Reactions

Palladium-carbon/montmorillonite (Pd-C/MMT) heterogeneous catalysts were prepared by carbonization of chitosan in palladium-chitosan/montmorillonite (Pd-CS/MMT) composites under a N₂ atmosphere. The main purpose of this study was to determine the effects of the carbonization temperature (250, 450, and 650°C) on the material microstructure and its catalytic performance. X-ray diffraction patterns revealed that the formation of an intercalation of the carbonaceous material between the clay mineral layers which was also confirmed by Fourier transform infrared spectra results. The N content of the Pd-C/MMT catalyst decreased as the carbonization temperature was increased. Thermogravimetry curves revealed that the thermal stability of the Pd-C/MMT catalyst increased obviously as the carbonization temperature was increased. Pd nanoparticles, sized at about 20 nm, were mainly dispersed on the surface of the MMT, as observed by high-resolution transmission electron microscopy (HR-TEM). The prepared Pd-C/MMT catalysts had good catalytic activity when applied in Heck coupling reactions of aromatic halides and alkenes to produce aryl olefins. The relations between the recyclability and the material composition are discussed.