Mesoporous silica nanospheres supported atomically precise palladium nanocluster: Highly efficient and recyclable catalysts in the reduction of 4-nitrophenol and Heck reactions

Atomically precise palladium nanoclusters show great potential applications in the field of catalysis owing to its ultrasmall size and precise structure. This work, we report the mesoporous silica nanoparticles (MSNs) supported [Pd3Cl(PPh3)(3)(PPh2)(2)]Cl catalysts (denoted as Pd3Cl/MSNs) for the reduction of 4-nitrophenol and Heck coupling reactions of iodobenzene and styrenes. High uniform MSNs, with average diameter approximate to 110 nm, were prepared by sol-gel method, followed by Pd nanoclusters immobilization into the pore of MSNs. The MSNs supported Pd nanoclusters were well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR), and diffuse reflectance optical spectrum. The results indicated that Pd3Cl nanoclusters after immobilized into the pores of MSNs are intact and possess good dispersibility. The catalytic performance of as-prepared nanocomposites was evaluated by the reduction of 4-nitrophenol and Heck reactions. The 4-nitrophenol could be completely conversion to 4-aminophenol within 6 min. Meanwhile, the as-prepared Pd3Cl/MSNs exhibit excellent catalytic performance in the Heck reactions between iodobenzenes and styrenes. The high catalytic activity of Pd3Cl/MSNs could be attributed to the large surface area and unique geometric structure of as-prepared Pd nanoclusters. More importantly, the catalysts could be easily recycled by centrifugation and shows excellent reusability.