In Situ Confined Growth Based on a Self-Templating Reduction Strategy of Highly Dispersed Ni Nanoparticles in Hierarchical Yolk-Shell Fe@SiO2 Structures as Efficient Catalysts.

Ni-based magnetic catalysts exhibited moderate activity, low cost, and magnetic reusability for hydrogenation reactions. However, Ni nanoparticles anchored on magnetic supports suffer commonly from undesirable agglomeration during catalytic reactions due to the relatively weak affinity of magnetic support to Ni nanoparticles. A hierarchically yolk-shell Fe@SiO2/Ni catalyst with an inner movable Fe core and an ultrathin SiO2/Ni nanosheets-assembled shell was synthesized via a self-templating reduction strategy with the hierarchically yolk-shell Fe3O4@nickel silicate nanocomposite as the precursor. Spatial confinement of highly dispersed Ni nanoparticles of the mean size of 4 nm into ultrathin SiO2 nanosheets of the 2.6-nm thickness could not only prevent their agglomeration during catalytic transformations but also expose abundant active Ni sites accessible to the reactants. Moreover, the large inner cavities and interlayer space among the assembled ultrathin SiO2/Ni nanosheets provide suitable mesoporous channels for the diffusion of the reactants toward active sites. As expected, the Fe@SiO2/Ni catalyst displays high activity, high stability and magnetic recoverability for the reduction of nitroaromatic compounds. In particular, the Ni-based catalyst maintained the conversion of 4-Nitroamine of over 98% and preserved the initial yolk-shell structure without any obvious aggregation of Ni nanoparticles after over ten catalytic cycles, confirming the high structural stability of the Ni-based catalyst.