Pd–PPy nanocomposite on the surface of carbon nanotubes: synthesis and catalytic activity

Abstract : In the presence of carbon nanotubes (CNTs), palladium (Pd)-polypyrrole (PPy)@CNT nanocomposites have been synthesized by way of one-pot and one-step colloidal synthesis from a solution of a palladium inorganic salt and organic pyrrole as monomeric precursor to PPy. This efficient method leads to the growth of nanoparticles of the palladium inorganic component distributed inside a polymer matrix supported on CNTs. After characterization, palladium-PPy@CNT nanocomposites have been employed as efficient heterogeneous catalysts for direct C-H bond functionalization toward C-C bond coupling formation. The notable catalytic activity of the palladium-PPy@CNT nanocomposite decreased with successive catalytic cycles when using the same portion of the composite. This was attributed to palladium redistribution inside the PPy matrix, which occurs by way of a specific mechanism involving the reaction solvent and the composite during C-C coupling reaction. This mechanism is recrystallization of palladium nanoparticles in conductive PPy matrix. Nevertheless, the use of palladium-PPy@CNT nanocomposite in first cycle of investigated catalytic reaction facilitates C-C bond coupling formation: reaction occurs at lower temperature in comparison with homogeneous catalysts.