Multifunctional catalysts based on palladium nanoparticles supported on functionalized halloysites: Applications in catalytic C-C coupling, selective oxidation and dehalogenation reactions

Abstract

A series of hybrid catalysts of the type, support-ligand-Pd (Sup-L-Pd), has been prepared and characterized and their activity in C-C coupling (Suzuki-Miyaura), selective oxidations and dehalogenation‑hydrogenation processes studied. The hybrid Sup-L-Pd catalysts are made up of (i) different nano-sized supports, such as halloysite nanotubes (HNTs), SiO2, Al2O3 and mesoporous silica nanoparticles (MSNs), (ii) ligands (L) with N-, S- or P-donor atoms and (iii) different quantities of Pd. Several combinations of support, ligand, and Pd quantity were used to determine the optimal composition of the nanostructured systems for the proposed catalytic reactions. The system based on HNTs functionalized with 2-(diphenylphosphino)ethyltriethoxysilane (PPETS) and 0.25% wt. Pd (HNTs-PPETS-Pd0.25) showed the most promising catalytic behaviour with multifunctional applicability in different catalytic processes and potential reusability. This catalyst gave turnover frequency (TOF) values of up to 155 h−1 in catalytic Suzuki-Miyaura C-C coupling reactions, up to 43 h−1 in selective catalytic oxidations and up to 65 h−1 in dehalogenation‑hydrogenation processes of halogenated aromatic compounds. Furthermore, the system demonstrated in the different catalytic reactions, good recyclability after consecutive cycles with low Pd leaching.