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Using a mixture of NO + O2 as the oxidant enabled the direct selective oxidation of methane to dimethyl ether (DME) over Pt/Y2O3. The reaction was carried out in a fixed bed reactor at 0.1 MPa over a temperature range of 275–375 °C. During the activity tests, the only carbon‐containing products were DME and CO2. The DME productivity (μmol gcat−1 h−1) was comparable to oxygenate productivities reported in the literature for strong oxidants (N2O, H2O2, O3). The NO + O2 mixture formed NO2, which acted as the oxygen atom carrier for the ultimate oxidant O2. During the methane partial oxidation reaction, NO and NO2 were not reduced to N2. In situ FTIR showed the formation of surface nitrate species, which are considered to be key intermediate species for the selective oxidation.

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Identification of methane (CH 4 ) activation sites on solid catalysts in CH 4 oxidation is crucial to provide understanding for the conversion of CH 4 to valuable oxygenates and thus has been a subject of intensive research. It has been suggested in many experimental and theoretical studies that oxidized metal sites, i.e., cationic sites, are responsible for CH 4 activation. However, clear spectroscopic evidence for this has been lacking. Here, we show that CH 4 is activated on the cationic sites, which was demonstrated by examining the oxidation processes of CH 4 to CO with nitrates (NO 3 − ) on a titania-supported platinum (Pt/TiO 2 ) sample. The reaction was analyzed by in situ Fourier transform infrared (FTIR) spectroscopy and in situ X-ray absorption near edge structure (XANES) measurement. It was found that upon the formation of NO 3 − on the sample, cationic sites (Pt 2+ ) form and CH 4 was converted to CO on Pt 2+ at 220 °C and then on metallic sites (Pt 0 ) at 270 °C. The switch of the CO formation sites is attributed to the conversion of Pt 2+ to Pt 0 during the oxidation reaction. The results indicate that Pt 2+ is the site for CH 4 activation.