Operando Observation of Hydrogenation of Carbon Dioxide by Near Ambient Pressure X-ray Photoelectron Spectroscopy

Abstract

Hydrogenation of carbon dioxide (CO₂) on copper/zinc oxide-based catalysts was investigated using near-ambient pressure X-ray photoelectron spectroscopy (AP-XPS). An initial hydrogenation step of CO₂ to formate was studied using Zn-deposited single-crystal Cu surfaces. CO₂ activation on the model catalysts leads to the formation of carbonates (CO₃) on the surface in the presence of near-ambient pressure CO₂ and hydrogen (H₂). The addition of a small amount of water to the feed gas enhances the hydrogenation of CO₂ into formate. This indicates that hydroxyl produced through dissociative adsorption of water is a source for the CO₂ hydrogenation observed under the present reaction conditions. We also performed operando spectroscopy of an industrial catalyst for methanol synthesis at higher pressure to reveal the chemical states of the catalyst and adsorbed intermediates during the catalytic reaction. In-situ formation of active catalytic sites was detected by operando hard X-ray photoelectron spectroscopy. Analysis of the reaction products in the presence of CO₂ and H₂ gases shows the formation of methanol and CO. The rate of methanol synthesis correlates with the dynamic changes in the chemical states of the catalyst, and the reaction intermediates adsorbed on the catalyst.