Effect of Oxygen on the Oxidation of Methane with Hydrogen Peroxide to Methanol in the Presence of Glutathione-Stabilized Gold Nanoclusters

The catalytic activity of glutathione-stabilized gold thiolate nanoclusters (1–2 nm) in the oxidation of methane with H2O2 and air oxygen in aqueous medium at 70°C in 30 atm CH4 was studied. The ratio and yield of the oxidation products CH3OH and CH3OOH depends on the content of H2O2 and oxygen in the reactor. At increased partial pressure of oxygen, the total yield of products increases compared with the total yield of independent oxidations with H2O2 or O2 at 5 atm of air, but decreases at 10 atm. A molecular mechanism of methane oxidation was proposed, which describes well the kinetic curves of accumulation and consumption of CH3OH and CH3OOH and the effect of oxygen on their yield. A molecular model of active site was proposed based on the literature data about the structure of glutathione-stabilized Au25 clusters and the results of quantum chemical modeling. The experiments with re-introduction of the gas phase and renewal of the H2O2 content demonstrated 100% conservation of the catalytic activity. The yield of CH3OH reached 60 mol per mole of Au25 clusters.