Isolated Fe Sites in Metal Organic Frameworks Catalyze the Direct Conversion of Methane to Methanol

Abstract

Hybrid materials bearing organic and inorganic motives have been extensively discussed as playgrounds for the implementation of atomically resolved inorganic sites within a confined environment, with an exciting similarity to enzymes. Here, we present the successful design of a site-isolated mixed-metal Metal Organic Framework that mimics the reactivity of soluble methane monooxygenase enzyme and demonstrates the potential of this strategy to overcome current challenges in selective methane oxidation. We describe the synthesis and characterisation of an Fe-containing MOF that comprises the desired antiferromagnetically coupled high spin species in a coordination environment closely resembling that of the enzyme. An electrochemical synthesis method is used to build the microporous MOF matrix while integrating the atomically dispersed Fe active sites in the crystalline scaffold. The model mimics the catalytic C-H activation behaviour of the enzyme to produce methanol, and shows that the key to this reactivity is the formation of isolated oxobridged Fe units.

Selective Aerobic Oxidation of Cumene to Cumene Hydroperoxide over Mono- and Bimetallic Trimesate Metal–Organic Frameworks Prepared by a Facile “Green” Aqueous Synthesis

“…It is well known that site isolation can be crucial in determining the observed catalytic properties of a material. [35][36][37] This is also the present case for the aerobic oxidation of cumene. Once a CHP molecule is formed in the main reaction, it can either desorb into the liquid phase, or it can undergo secondary oxidation or decomposition events at the surface of the catalyst that will consume CHP (decreasing the final CHP selectivity of the overall catalytic process).…”

Identifying promising metal–organic frameworks for heterogeneous catalysis via high‐throughput periodic density functional theory

“…In addition to being more kinetically reactive than N 2 O, the standard enthalpy of reaction for MOF + H 2 O 2 → MOF−O + H 2 O compared to MOF + N 2 O → MOF−O + N 2 is more thermodynamically favorable by 82 kJ/mol at the PBE‐D3(BJ) level of theory. H 2 O 2 has recently been used as the oxidant in the conversion of methane to methanol with Fe‐containing Al‐MIL‐53 as well as graphene‐confined single Fe atoms and multiple works involving cation‐exchanged zeolites . The use of other strong oxidizing agents is also likely worth considering for the purposes of gaining experimental insight into oxidative C—H bond activation on MOF‐supported metal‐oxo species.…”

“…As a proof‐of‐concept, we use this HT workflow to screen MOFs with coordinatively unsaturated metal sites, also known as open metal sites (OMSs), for oxidative C—H bond activation. Due to the large economic demand for a catalyst that can directly convert methane to methanol and motivated by prior work involving MOFs for methane conversion, we specifically consider the partial oxidation of methane as the reaction of interest. In the process, we demonstrate the feasibility of a HT‐DFT screening workflow for MOF catalysis and make several recommendations for future work involving HT‐DFT screening studies of MOFs.…”

Metal–Organic Frameworks Encapsulating Active Nanoparticles as Emerging Composites for Catalysis: Recent Progress and Perspectives

“…Until now there are more than 20 000 MOFs reported and some of them exhibit intriguing catalytic performances via thermo‐, photo‐ or electrodriven modes, which are generally implemented by metal node, functional organic linker or both . As for metal nodes, they are commonly associated with transition metals that likely introduce Lewis acidity, since several coordination positions of the metal centers are often occupied by solvent molecules that can be removed by heating or evacuation while keeping their frameworks. Furthermore, these metal nodes can undergo redox catalysis or promote coupling reactions .…”