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.

Multi-walled carbon nanotubes (MWNTs) with different defect density and oxygen-containing groups have been prepared, and they were utilized as the carriers of supported palladium catalysts for Heck synthesis. This work was proved the interaction between palladium sites and carrier carbon atoms could be largely enhanced by introducing defects and oxygen groups into the MWNT carrier system. Meanwhile, defects and oxygen-functional groups are assisted to improve the stability and reusability of these Pd-MWNT catalysts during the Heck reaction process.Figure optionsDownload high-quality image (182 K)Download as PowerPoint slideHighlights
► MWNTs with different defects and oxygen-functional groups densities have been prepared as new carriers for Pd/CNT Heck catalysts.
► Pd/CNTs catalysts were utilized for Heck synthesis.
► Higher defects and oxygen-functional groups on MWNTs contributed to higher Pd dispersion.
► The interaction of palladium active sites and defected MWNTs supports were further investigated by DFT molecular simulation.