Unveiling the catalytic potential of the Fe(iv)oxo species for the oxidation of hydrocarbons in the solid state

Abstract

We present the computational study of the ferryl-catalysed oxidation of methane into methanol in a solid-state system, the metal-organic framework MOF-74 with Fe(iv)O moieties in its cavities. We use spin-polarisedab initiomolecular dynamics at the hybrid HSE06 level of theory to simulate this process as three consecutive steps: the hydrogen abstraction from methane by Fe(iv)O, the rebound of the resulting CH3˙ radical to form a methanol molecule, and the detachment of the product from the reactive site. Our computational approach accounts for both enthalpic and entropic effects at room temperature. The calculations indicate that the overall oxidation process occurs with a free energy barrier of 95.6 kJ mol−1, with the detachment of methanol as the rate-determining step. For the abstraction step, we estimate a free energy barrier of 51.1 kJ mol−1at 300 K and an enthalpy barrier of 130.3 kJ mol−1, which indicates the presence of a substantial entropic contribution. van der Waals dispersion interactions play also a significant role in the overall reaction energetics. Our study suggests the potential applicability of metal-organic frameworks in the industrial production of fuels from saturated hydrocarbons and indicates that it is necessary to further investigate whether other factors, such as stability and easy regeneration, favour these materials.