In Situ Confined Growth Based on a Self-Templating Reduction Strategy of Highly Dispersed Ni Nanoparticles in Hierarchical Yolk-Shell Fe@SiO Structures as Efficient Catalysts.

Ni-based magnetic catalysts exhibit moderate activity, low cost, and magnetic reusability in hydrogenation reactions. However, Ni nanoparticles anchored on magnetic supports commonly suffer from undesirable agglomeration during catalytic reactions due to the relatively weak affinity of the magnetic support for the Ni nanoparticles. A hierarchical yolk-shell Fe@SiO /Ni catalyst, with an inner movable Fe core and an ultrathin SiO /Ni shell composed of nanosheets, was synthesized in a self-templating reduction strategy with a hierarchical yolk-shell Fe O @nickel silicate nanocomposite as the precursor. The spatial confinement of highly dispersed Ni nanoparticles with a mean size of 4 nm within ultrathin SiO nanosheets with a thickness of 2.6 nm not only prevented their agglomeration during catalytic transformations but also exposed the abundant active Ni sites to reactants. Moreover, the large inner cavities and interlayer spaces between the assembled ultrathin SiO /Ni nanosheets provided suitable mesoporous channels for diffusion of the reactants towards the active sites. As expected, the Fe@SiO /Ni catalyst displayed high activity, high stability, and magnetic recoverability for the reduction of nitroaromatic compounds. In particular, the Ni-based catalyst in the conversion of 4-nitroamine maintained a rate of over 98 % and preserved the initial yolk-shell structure without any obvious aggregation of Ni nanoparticles after ten catalytic cycles, which confirmed the high structural stability of the Ni-based catalyst.