fig3

Figure 3. (A) An HAADF-STEM image of FeN₄/GN-2.7. The red circles show some single iron atoms in the matrix of graphene nanosheets. The inset presents the model of FeN₄/GN; (B) ¹³C NMR spectra obtained from typical reaction products of methane oxidation; (C) A scheme of the designed in operando TOF-MS^[17]. Copyright 2018, Elsevier. HAADF-STEM: High-angle annular dark-field scanning transmission electron microscopy; FeN4: iron coordinated with four nitrogen atoms; GN: graphene nanosheets; NMR: nuclear magnetic resonance; TOF-MS: time-of-flight mass spectrometry.