Porous hierarchical nickel nanostructures and their application as a magnetically separable catalyst

Abstract

A convenient template- and surfactant-free strategy has been developed to prepare porous hierarchical Ni nanostructures by directly calcining the nickel-based flower-like precursor in Ar. The precursor is preformed by refluxing the solution of nickel nitrate and the co-precipitators of hexamethylenetetramine and oxalic acid at 100 °C for 6 h. The unique Ni nanostructures are composed of porous sheets of several nanometers in thickness with a wide pore size distribution of 5–100 nm, with a Brunauer–Emmett–Teller specific surface area up to 24.5 m² g⁻¹. The formation process has been in situ examined by thermogravimetry–differential scanning calorimetry–mass spectroscopy, which illuminates the continuous generation of Ni species with the simultaneous release of gaseous species from decomposition and/or reduction of the precursor. Coupled with the good soft ferromagnetism, the porous Ni nanostructures with high surface area have great potential as a magnetically separable catalyst, as demonstrated in the excellent performance for the selective hydrogenation of acetophenone to 1-phenylethanol at 100 °C.