The aerobic, selective oxidation of methane to C 1 -oxygenates remains a challenge, due to the more facile, consecutive oxidation of formed products to CO 2 . Here, we report on the aerobic selective oxidation of methane under continuous flow conditions, over platinum-based catalysts yielding formaldehyde with a high selectivity (reaching 90 % for Pt/TiO 2 and 65 % over Pt/ Al 2 O 3 ) upon co-feeding water. The presence of liquid water under reaction conditions increases the activity strongly attaining a methane conversion of 1-3 % over Pt/TiO 2 . Density-functional theory (DFT) calculations show that the preferential formation of formaldehyde is linked to the stability of the di-σ-hydroxy-methoxy species on platinum, the preferred carbon-containing species on Pt( 111) at a high chemical potential of water. Our findings provide novel insights into the reaction pathway for the Pt-catalysed, aerobic selective oxidation of CH 4 .

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The aerobic, selective oxidation of methane to C1‐oxygenates remains a challenge, due to the more facile, consecutive oxidation of formed products to CO2. Here, we report on the aerobic selective oxidation of methane under continuous flow conditions, over platinum‐based catalysts yielding formaldehyde with a high selectivity (reaching 90 % for Pt/TiO2 and 65 % over Pt/Al2O3) upon co‐feeding water. The presence of liquid water under reaction conditions increases the activity strongly attaining a methane conversion of 1–3 % over Pt/TiO2. Density‐functional theory (DFT) calculations show that the preferential formation of formaldehyde is linked to the stability of the di‐σ‐hydroxy‐methoxy species on platinum, the preferred carbon‐containing species on Pt(111) at a high chemical potential of water. Our findings provide novel insights into the reaction pathway for the Pt‐catalysed, aerobic selective oxidation of CH4.

The direct formation of formaldehyde in the selective, aerobic oxidation of methane in the presence of liquid water at ca. 498 K has recently been described. One of the intriguing observations in the aerobic oxidation of methane over platinum in the presence of water is the absence of the typically observed negative selectivity-conversion dependency (up to a methane conversion of 1 %). In this perspective, the main differences between this route and other methods for the selective oxidation of methane are being described. Possible reaction pathways for the formation of formaldehyde are discussed. Further developments for this newly developed methane activation route are highlighted.

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