Voltage-Gated Electrocatalysis of Efficient and Selective Methane Oxidation by Tricopper Clusters under Ambient Conditions

Selective methane oxidation is difficult chemistry. Here we describe a strategy for the electrocatalysis of selective methane oxidation by immobilizing tricopper catalysts on the cathodic surface. In the presence of dioxygen and methane, the activation of these catalysts above a threshold cathodic potential can initiate the dioxygen chemistry for O atom transfer to methane. The catalytic turnover is completed by facile electron injections into the tricopper catalysts from the electrode. This technology leads to dramatic enhancements in performance of the catalysts toward methane oxidation. Unprecedented turnover frequencies (>40 min^-1) and high product throughputs (turnover numbers >30 000 in 12 h) are achieved for this challenging chemical transformation in water under ambient conditions. The technology is green and suitable for on-site direct conversion of methane into methanol.

Role of catalytic nitrile decomposition in tricopper complex mediated direct partial oxidation of methane to methanol

Synthetic homogeneous system known to date performing methane to methanol conversion using O₂ as terminal oxidant is unique and based on copper complex with piperazine-based ligand (Cu₃L in Fig. 1) in a medium of acetonitrile. Prior work have shown that in order to achieve catalytic turnover, hydrogen peroxide is needed to regenerate the active site. We show in this paper that reaction solvent based on organic nitrile decompose concurrently with methane activation and that in the absence of either acetonitrile, Cu complex or hydrogen peroxide, the catalytic turnover does not happen. We show in this manuscript that the direct methane oxidation to methanol might have been mediated by catalytic Radziszewski oxidation between acetonitrile and H₂O₂. Additionally we have discovered that in the absence of methane, peroxide mediated acetonitrile decomposition also makes methanol via a background reaction which was hitherto unknown.

Catalytic machinery of methane oxidation in particulate methane monooxygenase (pMMO)

In this focused review, we portray the recently reported 2.5 Å cyro-EM structure of the particulate methane monooxygenase (pMMO) from M. capsulatus (Bath). The structure of the functional holo-pMMO near atomic resolution has uncovered the sites of the copper cofactors including the location of the active site in the enzyme. The three coppers seen in the original X-ray crystal structures of the enzyme are now augmented by additional coppers in the transmembrane domain as well as in the water-exposed C-terminal subdomain of the PmoB subunit. The cryo-EM structure offers the first glimpse of the catalytic machinery capable of methane oxidation with high selectivity and efficiency. The findings are entirely consistent with the biochemical and biophysical findings previously reported in the literature, including the chemistry of hydrocarbon hydroxylation, regeneration of the catalyst for multiple turnovers, and the mechanism of aborting non-productive cycles to ensure kinetic competence.