Using ambient pressure XPS (APXPS), we explored carbon dioxide (CO2) adsorption and CO2 hydrogenation on Pt(1 1 1) single crystal surface to observe the activation of CO2 and the subsequent reaction mechanism. In pure CO2, we observed CO adsorbates and adsorbed oxygen on Pt(1 1 1) derived from CO2 dissociation at room temperature. The introduction of H2 (at a pressure ratio of 1:1 (H2:CO2)) increased the production of CO across all temperatures by facilitating the removal of surface oxygen. As a consequence, the surface could expose sites that could then be utilized for producing CO. Under these conditions, the reverse water–gas shift (RWGS) reaction was observed starting at 300 oC. At higher H2 partial pressure (10:1 (H2:CO2)), the RWGS reaction initiated at a lower temperature of 200 oC and continued to enhance the conversion of CO2 with increasing temperatures. Our results revealed that CO2 was activated on a clean Pt(1 1 1) surface through the dissociation mechanism to form adsorbed CO and O at room temperature and at elevated temperatures. Introducing H2 facilitated the RWGS as adsorbed oxygen was consumed continuously to form H2O, and adsorbed CO desorbed from the surface at elevated temperatures. This work clearly provides direct experimental evidence for the surface chemistry of CO2 dissociation and demonstrates how hydrogen impacts the RWGS reaction on a platinum surface.

Converting carbon dioxide (CO₂) into liquid fuels and synthesis gas is a world-wide priority. But there is no experimental information on the initial atomic level events for CO₂ electroreduction on the metal catalysts to provide the basis for developing improved catalysts. Here we combine ambient pressure X-ray photoelectron spectroscopy with quantum mechanics to examine the processes as Ag is exposed to CO₂ both alone and in the presence of H₂O at 298 K. We find that CO₂ reacts with surface O on Ag to form a chemisorbed species (O = CO₂^δ-). Adding H₂O and CO₂ then leads to up to four water attaching on O = CO₂^δ- and two water attaching on chemisorbed (b-)CO₂. On Ag we find a much more favorable mechanism involving the O = CO₂^δ- compared to that involving b-CO₂ on Cu. Each metal surface modifies the gas-catalyst interactions, providing a basis for tuning CO₂ adsorption behavior to facilitate selective product formations.