Fig. 1: Synthesis method and structural diagrams of the nanocatalysts.

a Synthesis route of the hydroxylated CuNi-MA catalyst. b TEM and c HRTEM image and the corresponding fast Fourier transform patterns (inset). d Mg, Al, Cu and Ni elemental mapping images of Cu3Ni-MA. e AC-HAADF-STEM images and particle size distribution (inset). f–h AC-HAADF-STEM image and the corresponding EDS mapping/line scan (inset). The ultra-fine CuNi nanoparticles (NPs) as shown in white circles. The scale bars in b–d, f–h are 20 nm, 2 nm, 200 nm, 10 nm, 3 nm, 5 nm, respectively. i XRD pattern and partial enlargement (right side) of Cu-MA, Cu3.9Ni0.1-MA, Cu3.5Ni0.5-MA, Cu3Ni-MA, Cu2Ni2-MA and Ni-MA. j, k Cu 2p and Ni 2p XPS spectra of Cu3Ni-MA, Cu-MA and Ni-MA.