Stabilization of palladium nanoparticles inside chitosan derived N-doped carbon nanofibers for Heck reaction

We report the synthesis of palladium nanoparticles encapsulated N-doped carbon nanofibers derived from environmentally benign chitosan. Palladium salt was incorporated into the chitosan/sodium polyacrylate composite nanofibers by electrospinning, followed by carbonization under argon atmosphere to prepare palladium encapsulated mesoporous carbon nanofibers (Pd@Carbon). SEM images shows that the fibrous structures were well retained after carbonization processes. The Raman spectra demonstrates that the ratio of graphite carbon were increased with the carbonization temperature. X-ray powder diffraction and transmission electron microscopy analysis shows that PdO and Pd nanoparticles were formed in the carbon fibers and their sizes grew with the carbonization temperature. The sizes and concentrations of submicroscopic pores inside the nanofibers were analyzed by nitrogen adsorption/desorption experiments and positron annihilation lifetime spectra. Heck reaction catalysis result shows that high carbonization temperature could improve the catalytic activity of Pd@Carbon nanofibers and the nanofibers carbonized at 800°C had the highest catalytic activity. Moreover, the catalytic activity of these novel composite nanofibers was well retained even after recycling for 13 times. The excellent catalytic performance of this fibrous palladium catalyst can be attributed to the N-rich carbon nanofibers and encapsulation of palladium active species inside the ultrathin mesoporous carbon fibers.