Nickel hierarchical flower-like nanostructures: Controlled synthesis and catalytic hydrogenation of toluene

Nickel (Ni) nanocrystals with a flower-like shape were successfully fabricated through a low temperature solution-phase approach without using any template or surfactant. The structures and morphologies of the as-synthesized Ni nanocrystals were systematically characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller surface analysis. Further, the magnetic property was also analyzed using a vibrating sample magnetometer (VSM). The characterization results showed that the entire structure of the products with diameter of around 500 nm was composed of several nanocones connected with each other through the center to form the three-dimensional hierarchical flower-like structures. Moreover, the orientation and morphology of the products could be carefully controlled by adjusting the reaction temperature, the growth time, and the reaction solvent. Furthermore, a possible formation mechanism of the hierarchical flower-like Ni nanostructures was also proposed based on the detailed characterization analysis. Besides, the series of Ni nanocrystals was studied for the catalytic hydrogenation of toluene to methylcyclohexane. It was found that the hierarchical flower-like Ni nanostructures obtained at 80 °C for 2 h showed an optimal catalytic performance among all the Ni catalysts tested, and correspondingly a 100% hydrogenation of toluene was achieved with in 30 min under the relatively mild reaction conditions. The merits including excellent durability, sound productivity, and superior catalytic performance make the hierarchical Ni nanocrystals as promising catalysts for the practical industrial application.