Application of near ambient pressure gas-phase X-ray photoelectron spectroscopy to the investigation of catalytic properties of copper in methanol oxidation

•Selective oxidation of CH3OH to CH2O over a Cu foil has been studied by in situ gas phase XPS.•C1s and O1s spectra were used for identification of reagents and reaction products in a gas phase.•Catalytic data (conversions and reaction products yields) calculated from XPS spectra are in a good agreement with QMS results.•The possible reasons of the observed variations in reaction mechanism have been discussed. Application of near ambient pressure (NAP) X-ray photoelectron spectroscopy for characterization of catalytic properties of a heterogeneous catalyst through measurement and analysis of the core-level spectra from gas phase constituents, which become measurable in submillibar pressure range, has been demonstrated for the reaction of methanol oxidation over polycrystalline copper foil. To improve the accuracy of quantitative analysis of the gas phase signals for the routine XPS spectrometer with double Al/Mg anode used in these experiments, the sample was removed from XPS analysis zone, but it was still located in high-pressure gas cell. As consequence, only gas phase peaks from reagents and reaction products have been observed in XPS spectra. Quantitative analysis of the spectra has allowed us to calculate conversions of the reagents and yields of the reaction products, or, other words, to characterize the catalytic properties of the catalyst and to track their changes with temperature. Further comparison of the catalytic properties with concentration of the surface species measured by in situ XPS in separate experiments, but under the same conditions, gives a possibility to discuss the reaction mechanisms.