Defect Engineering in Graphene-Confined Single-Atom Iron Catalysts for Room-Temperature Methane Conversion

Direct conversion of methane to high-value-added chemicals with oxidants, such as H2O2, O-2, and so forth, without going through the intermediate syngas production step is potentially more energy efficient, cost-effective and environmentally friendly. Recent experiments have demonstrated that graphene-confined single-atom Fe (FeN4) catalysts could efficiently catalyze direct methane conversion to C1 oxygenates at room temperature. However, the methane conversion rates of FeN4 catalysts are far from satisfactory. Motivated by the enormous potential of defect engineering to advance rational catalyst design, we carry out first-principle computations to systematically explore the impact of various defects, including vacancies and substitutional doping of heteroatoms, on the catalytic activities of FeN4 catalysts for the direct conversion of methane to C1 oxygenates. Encouragingly, we find the C vacancies (FeN4-V-6r and FeN4-V-5r) and P dopant (P-O/FeN4) adjacent to FeN4 centers can significantly improve the methane conversion activities of FeN4 catalysts. Our results show that the methane activation rates of FeN4-V-6r, FeN4-V-5r, and P-O/FeN4 are 1.7 x 10(4), 2.4 x 10(3), and 5.3 x 10(3) times higher than that of perfect FeN4 catalyst, respectively. The improved catalytic performance of these three FeN4 catalysts stem from their moderate formation energy of O-FeN4-O active site (G(f)), which is used as a key descriptor for characterization of methane conversion activity. This study brings new understanding of the potential impact of controlled defect engineering on direct methane conversion using FeN4 catalysts, revealing a promising avenue to boost the catalytic performance for room-temperature methane conversion.