Direct conversion of methane to methanol over nano-[Au/SiO2] in [Bmim]Cl ionic liquid

This article describes a green chemical process employing nano-particle gold as the catalyst and ionic liquids (IL) as solvent for the methane oxidation. The catalytic reaction was carried out in a 100 ml autoclave filled with 2 MPa of CH4 gas, together with nano-particle gold supported on SiO2 as the catalyst, [Bmim]Cl as the solvent, trifluoroacetic acid (TFA) and trifluoroacetic anhydride (TFAA) as the acidic reagents, and K2S2O8 as the oxidant. The influence of the amounts of Au/SiO2 and the ionic liquid on the conversion of methane was investigated at reaction temperature of 90 °C. The main product is methanol, which exists as the methyl group of the methyl trifluoroacetate. In presence of 0.01 g Au/SiO2 and 1 g IL, the methane conversion is 24.9%, the selectivity of product is up to 71.5% and the yield is 17.8%. The selectivity of carbon dioxide is 1.6% and the yield is 0.6%. The selectivity of hydrogen is 0.4% and the yield is 0.1%. In the reaction system, the gold particles and IL can be recycled, which recovery is about 96.9%. The conversion of methane in the recycled system remains as high as 21.75%. The mechanism of methane to methano conversion, as well as the catalytic action of the nano-gold, was also discussed.

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► The process of methane conversion was a green chemical process.
► SiO2-supported nano-gold, dispersed in an ionic liquid, were used as the catalyst.
► The catalysis system (Au/IL) can be recycled and utilized.
► The main product is methanol.
► The methane conversion is 24.9%. The selectivity is 71.5%. The yield is 17.8%.