Effect of Oxygen on the Oxidation of Methane with Hydrogen Peroxide to Methanol in the Presence of Glutathione-Stabilize
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ct of Oxygen on the Oxidation of Methane with Hydrogen Peroxide to Methanol in the Presence of Glutathione-Stabilized Gold Nanoclusters S. A. Golovanovaa, A. P. Sadkova, and A. F. Shestakova, b, * aInstitute
of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, 142432 Russia Department of Fundamental Physical and Chemical Engineering, Moscow State University, Moscow, 119991 Russia *е-mail: [email protected]
b
Received May 30, 2019; revised December 24, 2019; accepted March 5, 2020
Abstract—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. Keywords: methane oxidation, gold nanoclusters, catalyst, methanol, oxygen, hydrogen peroxide, methyl hydroperoxide DOI: 10.1134/S0023158420040060
INTRODUCTION Selective oxidation of CH4 to CH3OH has been the subject of active research over the last decades. Despite the practical importance of the problem of obtaining valuable products from natural gas, so far there is no solution of this problem acceptable for use in manufacturing [1, 2]. Therefore, it is important to search for new effective catalysts for low-temperature methane oxidation [3–9]. The discovery of metalcomplex activation of aliphatic С–Н bonds under mild conditions (Shilov reaction) [4] indicated the possibility of direct low-temperature conversion of hydrocarbons into functionalized products using new coordination catalysts based on transition metals [10, 11]. The pioneering work of M. Haruta on low-temperature oxidation of CO revealed the chemical activity of gold in a finely dispersed state [12]. In accordance with his statement in [13], gold cluster chemistry later led to the discovery of new exciting areas of research with emphasis on dramatic changes in the reactivity of Au particles with a magic number of Abbreviations: NP, nanoparticle; GSH, glutathione; Au NCs, gold nanoclusters; DLS, dynamic light scattering; XRD, X-ray diffraction analysis.
atoms. Today it is known that gold compounds (complexes, clusters, and nanoparticles (NPs)) catalyze a wide range of chemical react
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