Fe/Fe3C@N-doped porous carbon microspindles templated from a metal–organic framework as highly selective and stable catalysts for the catalytic oxidation of sulfides to sulfoxides

Abstract

The preparation of efficient and recyclable solid catalysts exhibiting high activity and selectivity toward the target product is a prerequisite to enhance the overall efficiency of a catalytic process. Herein, we study a series of Fe/Fe3C-containing nitrogen-doped porous carbon microspindles (Fe/Fe3C@NC–x, where x stands for the pyrolysis temperature), which are core-/shell-structured hybrids, constructed by the pyrolysis of a metal–organic framework precursor as highly selective catalysts for the oxidation of sulfides to the corresponding sulfoxides under mild conditions. The Fe/Fe3C@NC–x microspindles comprising Fe and Fe3C nanocrystals inlaid in nitrogen-doped porous carbon shells are fabricated by the direct carbonization of NH2–MIL–88B(Fe) polyhedra at 500 °C–800 °C and under nitrogen atmosphere. Among the various investigated catalysts, the Fe/Fe3C@NC–600 microspindles exhibit the best catalytic activity, higher than those exhibited by the analogue Fe/Fe3C@C–600 without N doping and the commercial Fe2O3, Fe3O4, and Fe3C used for the catalytic oxidation of sulfides owing to the synergistic contribution of the Fe3C sites and adequate nitrogen doping in the porous carbon support. Furthermore, the magnetically separable properties of the Fe/Fe3C@NC–600 microspindles enable their convenient isolation from the reaction system using an external magnet, and they can be repeatedly used for six cycles without any loss in catalytic efficiency.