Selective Oxidation of Methane into Formic Acid over ZIF‐8‐Encapsulated Mononuclear Fe Species under Mild Conditions

Abstract

AbstractThe direct catalytic oxidation of methane into C1 oxygenates is a promising approach for methane valorization. However, the difficulties in CH4 activation and inhibition of over‐oxidation hinder the development of efficient catalysts for this transformation. Herein, highly dispersed Fe species confined by ZIF‐8 are developed for the direct transformation of methane into value‐added C1 oxygenates with H2O2 as oxidant at 323 K. The as‐obtained Fe‐ZIF‐8 can afford an optimal turnover rate (TOR) of ∼45 molC1 molFe−1 h−1. Note that the selectivity to HCOOH is ∼97 %, outstanding among the reported Fe‐based heterogeneous catalysts. Combined analysis of X‐ray photoelectron spectroscopy, X‐ray absorption spectroscopy, ultraviolet‐visible diffuse reflectance spectroscopy and 57Fe Mössbauer spectroscopy suggests that the catalytically active sites in Fe‐ZIF‐8 are mononuclear six‐coordinated Fe3+ species. The confinement of mononuclear Fe species within a porous metal‐organic framework material can provide an exquisite, enzyme‐like performance for highly selective oxidation of methane towards formic acid under mild conditions.