Porous hierarchical nickel nanostructures and their application as a magnetically separable catalystElectronic supplementary information (ESI) available: FTIR spectrum of the nanostructured precursor; two control experiments; characterizations of the porous NiO microflowers; typical SEM image of Ni-335 °C sample; in situ DTG curves and MS spectra by calcining the precursors in Ar and air; magnetic properties of the Ni nanostructures; characterization of Ni-335 °C catalyst after reaction. See DOI

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 m 2 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. Porous hierarchical Ni nanostructures are prepared by a convenient template/surfactant-free strategy and demonstrate excellent performance as magnetically separable catalysts.