CO2 Activation and Reaction on Zn-Deposited Cu Surfaces Studied by Ambient-Pressure X-ray Photoelectron Spectroscopy

The reaction of carbon dioxide (CO2) on Zn-deposited copper surfaces was systematically investigated by ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). In the presence of 0.8 mbar CO2 and 0.4 mbar H-2 gases, hydrogenation products are not observed; only carbonate is formed on Zn-deposited Cu(111) and Cu(997) surfaces. The formation rate of carbonate at 299 K is significantly faster on Zn/Cu(997) than that on Zn/Cu(111), indicating step sites are more reactive for CO2 activation than terrace sites. On the other hand, the addition of water in the feed gas leads to hydrogenation of CO2 to formate at sample temperatures around 400 K. This suggests that hydroxyl produced from dissociative adsorption of water is a source for the CO2 hydrogenation observed under the present reaction conditions. The reaction products such as carbonate and formate on the Zn/Cu(997) surface are more stable than those on the bare Cu(997) surface. In particular, formate remains on Zn-deposited Cu surfaces up to 473 K, which is close to the operation temperature of industrial Cu-ZnO catalysts. Therefore, one of the roles of Zn atoms on Cu surfaces is the stabilization of reaction intermediates formed from CO2.