Temperature-Tunable Selective Methane Catalysis on Au₂⁺: From Cryogenic Partial Oxidation Yielding Formaldehyde to Cold Ethylene Production

The catalytic partial oxidation of methane into valuable products is of great scientific importance and considerable industrial and economical interest. Particularly challenging is the direct and selective oxidation of methane with molecular oxygen at moderate temperatures in a “green”, sustainable, and ecological manner. A mixture of methane and molecular oxygen is shown to selectively convert into formaldehyde at temperatures below 250 K if mass-selected Au 2 + clusters are introduced into the gas mixture as catalysts. At higher temperatures O 2 does not adsorb readily on the gold clusters, and catalyzed cooperative dehydrogenation of methane molecules results in the formation of ethylene. Gas-phase reaction kinetics measurements in a radio frequency ion trap under multicollision conditions, in conjunction with first-principles simulations, reveal mechanistic details of the temperature-tunable coupled catalytic cycles. The discovery of temperature-controlled dehydrogenation/partial-oxidation selective catalytic cycles is an important step in the rational design of gold-based low temperature oxidation catalysts.