Graphene/pyrrolic-structured nitrogen-doped CNT nanocomposite supports for Pd-catalysed Heck coupling and chemoselective hydrogenation of nitroarenes

Abstract

This work focused on the synthesis of 3D Pd-based nanocomposites which were tested in Heck coupling reactions and for the hydrogenation of nitroarenes. This was achieved by fabrication of graphene oxide/nitrogen-doped carbon nanotubes (G/N-CNTs) by mechanical grinding of 2D graphene oxide (GO) and 1D oxygen-treated nitrogen-doped CNTs (N-CNTs-OT) in a 3:1 ratio, respectively. The fabrication of G/N-CNTs is to overcome the habitual aggregation and restacking of graphene sheets. Palladium nanoparticles (Pd NPs) were deposited on the 3D G/N-CNTs nanocomposites via metal organic chemical vapour deposition method. The 3D Pd-based nanocomposites were characterized by TEM, SEM, HRTEM, XRD, TGA, XPS, ICP-OES, elemental analysis, BET analysis and Raman spectroscopy. For the Heck coupling reactions, aryl halides, olefins and 3D Pd-based nanocomposites were mixed in a suitable solvent and the reaction carried under microwave irradiation. The chemoselective hydrogenation of nitroarenes was done with dry ethanol in a Paar reactor, purged with H2 gas. These catalysts demonstrate excellent activity and selectivity in both reactions. The remarkable activity of the 3D Pd-based nanocomposites in Heck reactions and hydrogenation of nitroarenes may be attributed to the small particle size (3–10 nm) and a high degree of dispersion of Pd NPs. A comparative experiment was conducted with Pd/AC, Pd/CNTs, Pd/G/CNTs and Pd/rGO. Pd/G/N-CNTs-OT showed higher activity and selectivity than Pd/G/CNTs, Pd/G/N-CNTs, Pd/rGO and Pd/N-CNTs counterpart.