Recycling of CO2: Probing the Chemical State of the Ni(111) Surface during the Methanation Reaction with Ambient-Pressure X-Ray Photoelectron Spectroscopy

Using ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), we studied the adsorption and reactions of CO 2 and CO 2 + H 2 on the Ni(111) surface to identify the surface chemical state and the nature of the adsorbed species during the methanation reaction. In 200 mTorr CO 2 , we found that NiO is formed from CO 2 dissociation into CO and atomic oxygen. Additionally, carbonate (CO 3 2- ) is present on the surface from further reaction of CO 2 with NiO. The addition of H 2 into the reaction environment leads to reduction of NiO and the disappearance of CO 3 2- . At temperatures >160 °C, CO adsorbed on hollow sites, and atomic carbon and OH species are present on the surface. We conclude that the methanation reaction proceeds via dissociation of CO 2 , followed by reduction of CO to atomic carbon and its hydrogenation to methane.