Single-atomic-site iron on N-doped carbon for chemoselective reduction of nitroarenes

A facile, gram-scale and sustainable approach has been established for the synthesis of single-atomic-site iron on N-doped carbon (Fe-SA@NC-20A) via the pyrolysis of aniline modified FeZn-ZIFs, in which the synthesis of zeolitic imidazolate frameworks (ZIFs) can be accomplished in water at room temperature, and no acid etching is required. The as-synthesized catalyst exhibits better performance on the chemoselective hydrogenation of nitroarenes with a broad substrate scope (turnover frequency (TOF) up to 1,727 h(-1), 23 examples) than most of previously reported works. Based on high-angle annular dark field scanning transmission microscopy (HAADF-STEM) images in combination with X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), electron spin resonance (ESR), and Mossbauer spectroscopy, Fe is dispersed as single atoms via forming FeNx (x = 4-6). This work not only determines the active sites of Fe-SA@NC-20A for hydrogenation (FeN4), but also proposes tentative pathways for both N-H activation of hydrazine and the reduction of nitroarene on FeN4 site, both of which are the key steps for the hydrogenation of nitroarenes. In addition, this catalyst shows excellent stability, and no significant activity degradation is observed when recycling for 10 times or restoring in air for 2 months.