Palladium loaded on ZnO nanoparticles: Synthesis, characterization and application as heterogeneous catalyst for Suzuki–Miyaura cross-coupling reactions under ambient and ligand-free conditions

Abstract

Pd loaded ZnO nanoparticles have been explored as an efficient catalyst for Suzuki-Miyaura cross-coupling reactions under ambient and ligand-free conditions. For this purpose, the low temperature synthesis of ZnO nanoparticle was accomplished by the solution based approach using stoichiometric amount of zinc acetate and urea. The Pd/ZnO nanocrystalline catalyst was prepared by loading 3% PdCl2 on ZnO nanoparticles by simple wet impregnation technique. This catalyst efficiently performed Suzuki-Miyaura reactions with various ring substituted aryl bromides and boronic acids. The resultant Pd/ZnO nanocrystalline material conferred 97% yield under optimized reaction conditions. The nanostructured Pd loaded ZnO catalyst was characterized by XRD, FESEM, EDS, FETEM, STEM-BF-DF, XPS and BET techniques. XRD pattern of Pd/ZnO sample hints the presence of Pd as minor phase loaded on ZnO nanocrystalline material, while overall XPS analysis discloses effective loading of Pd (0) on ZnO surface. FESEM/TEM–EDS also revealed reasonable Pd loading on ZnO nanoparticles. The FETEM examination of unloaded ZnO and Pd loaded ZnO disclosed particle size in the range 25–40 nm. The nanocrystalline Pd/ZnO catalyst was reused without significant loss of catalytic activity. The present methodology is cost effective, environmentally friendly, easy to scale up and can become an alternative to homogeneous catalysis.