A promising approach for achieving a carbon-neutral society is to recycle CO2 instead of releasing it into the atmosphere. Due to the inertness of CO2, this is a difficult task, but already today, industrial production of methanol is performed over Cu-based catalysts with CO2 as the primary source of carbon. In order to facilitate the development of future catalysts recycling CO2 in different processes, we are studying the interaction between CO2 and Cu single crystals. Exposure of Cu(100) to O2 results in a c(2x2) structure of adsorbed O. When the coverage approaches 0.5 ML, however, it induces a missing-row (MR) reconstruction, where every fourth surface row of Cu is removed. With increasing O coverage, there is also a shift of the O 1s core level peak towards higher binding energy. The origin of this shift has not been satisfactory discussed in literature, but our interpretation is that it is caused by the reconstruction, which changes the coordination of the O atoms from 4 to 3 Cu atoms. At low pressures, exposure of Cu(100) to CO2 does not result in any significant adsorption, but at pressures in the order of 0.1 Torr, atomic oxygen is found on the surface. The figure shows in-situ APXPS results of the O 1s level during exposure to 0.3 Torr CO2 at 100°C and very similar results were found for exposures at 200°C and 300°C. The shift of the peak is obvious in the 2D plot in panel a, indicating that the growth of O structures is similar when CO2 is used as the O source instead of O2. In addition, the uptake curves in panel b shows that there are two different growth regimes with a drop in the adsorption speed at about 0.25 ML, which coincides with the start of the binding energy shift, followed by a smooth convergence towards what we assume is a saturation coverage of 0.5 ML. These results agree fairly well with a recent APXPS and HPSTM study by Eren et al. They, however, did not follow the CO2 adsorption live, and hence did not notice the different regimes in adsorption speed.

Dissociative adsorption of CO2 on Cu(100)

254th National Meeting (2017)

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