Hollow and Yolk-Shell Co-N-C@SiO2 Nanoreactors: Controllable Synthesis with High Selectivity and Activity for Nitroarene Hydrogenation.

The use of hollow and yolk-shell nanocomposites is an effective route to enhance catalytic performance. A strategy that allows precise control of the nanocomposites was developed to synthesize novel hollow and yolk-shell SiO2 nanoreactors of Co-N-C@SiO2, which used ZIF-67 as the hard template and also as the source for active sites. A size dependence of the nanoreactor structure was observed. Large size of ZIF-67 gave yolk-shell Y-Co-N-C@SiO2 while small size of crystals gave hollow H-Co-N-C@SiO2. The hydrogenation reaction results showed that the Co-N-C@SiO2 catalyst exhibited a high selectivity (>99%) to aniline and gave an activity (35.3 h-1) ∼3.3 times higher than that of Co/SiO2 (11.8 h-1). The excellent performance was attributed to that Co nanoparticles were doped in the N-C framework where they formed Co-Nx species and that the HSN had a void structure that had a reduced diffusion limitation.