Single-Atom Iron with Fe−S2o2 Structure as an Amphiphilic Catalyst for Enhanced Selective Oxidation of C−H Bonds

Abstract

Developing highly-efficient Fe-based single-atom catalysts (SACs) for the selective oxidation of C−H bonds to produce value-added aromatic ketones under mild conditions is still challenging. Herein, the construction of amphiphilic Fe SACs with electron-deficient Fe−S2O2 structure supported on porous S-doped lignin-derived carbon (Fe1/SLC) was achieved using a ball milling combined with impregnation method. The synergistic interaction between electron-deficient and ethylbenzene (EB)-water microinterfacial effects, which markedly enhanced the catalytic activity and acetophenone (AP) selectivity for the selective oxidation of ethylbenzene to acetophenone (OEB-A) under 60 °C for 12 h, obtaining an AP selectivity of 99.1% at 99.0% EB conversion and a high TOF of 2422.3 mmolEB gFe−1 h−1, both much higher than those of Fe1/LC and FeNPs/SLC, which surpassed most reported catalysts in similar reaction systems. Fe−S2O2 sites benefited the cleavage of TBHP to generate 1O2, •O2− and •OH radicals, where 1O2 was dominant, while •O2– and •OH performed a secondary role. Meanwhile, the amphiphilic property of Fe1/SLC induced by C−SOx−C structure heightened the catalytic activity and AP selectivity, which originated from the unique interfacial hydrogen-bonding interactions and polarity gradients effect. Furthermore, Fe1/SLC delivered excellent recyclability, long-term storage stability, and satisfactory universality. This work not only provides a promising and facile strategy to improve the catalytic activity and aromatic ketones selectivity for the selective oxidation of C−H bonds, but also open new avenue to the exploitation of waste biomass.

Keywords: Amphiphilic catalyst, Selective oxidation of C−H bonds, Single-atom catalysts, Heteroatom doping, Synergistic effect