Lawrence Berkeley National Laboratory

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.