Experimental and theoretical investigation on the interaction between palladium nanoparticles and functionalized carbon nanotubes for Heck synthesis

Multi-walled carbon nanotubes (MWNTs) with different defect density and oxygen-containing groups have been prepared and they were utilized as the carriers of palladium based catalysts for Heck synthesis. The catalytic activity, stability and Pd leaching were investigated. Furthermore, characterization techniques such as Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), High-resolution transmission electron microscope (HRTEM), X-ray diffractometer (XRD) and Density Functional Theory (DFT) simulation were employed to investigate the defects impacts on Pd/MWNTs catalysts. The results showed that Pd/MWNTs catalysts had good and similar activity under air atmosphere; while the Pd/MWNTs catalysts with higher defect density were more stable than that of lower defect density. The characterization results revealed that defects on CNTs carrier effectively suppressed the increase of Pd nanoparticle size. The DFT simulation proved that defects on CNTs promoted the redistribution of electrons, which enhanced the Pd–C interaction. Because the high surface energy of Pd nanoparticles was efficiently decreased, less Pd particle size could be found in the system with MWNTs of higher defects density. Meanwhile, defects played a role of new nucleation center for Pd deposition, which suppressed the increase of Pd particle size.