Synthesis of Ru/CoNi crystals with different morphologies for catalytic hydrogenation

Abstract

Cobalt–nickel alloy crystals with different morphologies, such as flower-like, column-like, mushroom-like and dendrite-like, were prepared by a facile hydrothermal or solvothermal reduction approach without the addition of any surfactant, using hydrazine hydrate as a reducing agent, ethanediamine as a capping agent and a mixture of nickel(II) chloride hexahydrate (NiCl2·6H2O) and cobalt(II) chloride hexahydrate (CoCl2·6H2O) as a precursor. The effect of hydrothermal temperature (120, 150 or 180 °C) and solvent (water or ethanol) on the shape of the CoNi crystals was investigated in this work. The corresponding Ru/CoNi catalysts (Ru-on-CoNi nanocrystals) were obtained via a galvanic replacement reaction. The sizes, element chemical states, morphologies and structures of the CoNi and Ru/CoNi samples were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and high-sensitivity low-energy ion scattering (HS-LEIS) techniques. The catalytic performance of the as-synthesized catalysts was evaluated by using the benzene hydrogenation reaction. The Ru/CoNi catalyst with a dendrite-like morphology exhibited the highest catalytic hydrogenation activity among the Ru/CoNi catalysts with different shapes. This was mainly due to its high Ru dispersion, many defect sites and positive synergistic effect compared with ruthenium, nickel and cobalt related species. Importantly, the cost of recycling the Ru/CoNi catalysts was relatively low because they could be recycled by magnetic separation.