Atomically Dispersed Fe-N5 Sites Anchored on 3D N-Doped Porous Carbon for Efficient Selective Oxidation of Aromatic Alkanes at Room Temperature.

Abstract

On account of the increasing demand for aromatic ketones and the challenging task of mass production in the chemical industry, efficient and sustainable catalysts are urgently needed to catalyze the conversion of aromatic alkyl compounds into high value-added products via the activation of C-H bonds. Herein, Fe single-site atoms anchored on a N-doped three-dimensional (3D) porous carbon nanostructure (Fe-MEG-800) synthesized through the self-assembly hydrothermal method are reported. Detailed characterization analyses, such as aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM), are employed to prove the isolated single Fe atom dispersing on the carbon nanostructure, along with X-ray absorption spectroscopy (XAS) and Mössbauer spectroscopy analysis confirming the Fe-N5 coordination structure. Furthermore, the 3D cross-linked structure not only provides an abundant open-framework structure for the mass transfer during the reaction but also facilitates the exposure of more active sites and promotes the reaction procedure. The as-prepared catalyst possesses high catalytic activity toward the C-H bond at room temperature. In the model reaction of oxidizing ethylbenzene (EB) to high-value acetophenone (AcPO), the conversion and the selectivity of the reaction are both over 99%. In addition, the catalyst also presents favorable stability with retaining high performance even after eight cycles. The possible adsorption sites of the reactant and oxidant are explored through density functional theory (DFT) calculations. Based on the analysis of experimental and theoretical results, a possible mechanism for the oxidation of EB to AcPO involving •OH, O2•-, and 1O2 is also proposed.