Surface Orientation and Pressure Dependence of CO₂ Activation on Cu Surfaces

Abstract

A fundamental understanding of interactions between catalysts and gas molecules is essential for the development of efficient heterogeneous catalysts. In this study, ambient pressure X-ray photoelectron spectroscopy (APXPS) and density functional theory (DFT) simulation were employed to investigate the activation of CO2 on Cu surfaces, which acts as a key step in the catalytic reduction of CO2. APXPS results show that CO2 is adsorbed as CO2 δ− on the Cu(111) surface under a pressure of 0.01 mbar at 300 K. Adsorbed CO2 δ− gets partially transformed into carbonate with an increase of pressure to 1 mbar due to the disproportionation reaction between CO2 molecules. Subsequent annealing of the Cu(111) surface in a CO2 atmosphere leads to the dissociation of CO2 δ− and carbonate, and a transformation to a chemisorbed oxygen covered surface occurred at 400 K and elevated temperatures. However, on the Cu(110) surface, the CO2 δ− gradually dissociates to CO and chemisorbed oxygen in the presence of 1 mbar of CO2 at room temperature. The self-deactivation of CO2 adsorption due to the atomic oxygen generated by CO2 dissociation is observed on both Cu(111) and Cu(110) surfaces. Moreover, these experimental results indicate that the Cu(110) surface is more active than the Cu(111) surface in breaking C–O bonds, which is consistent with the results of DFT simulations. Our findings indicate that the activation of CO2 on Cu surfaces is strongly surface orientation- and pressure-dependent, which is an important step to clarify CO2 activation mechanisms on Cu-based catalysts.

Impacts of the Catalyst Structures on CO2 Activation on Catalyst Surfaces

“…On both surfaces, atomic oxygen was generated that catalyzed the self-deactivation of CO 2 adsorption. The DFT results, which collaborated the experimental findings, further indicated that the Cu (110) surface was more active than the Cu (111) surface in breaking C-O bonds [95]. Comparing the adsorption of CO 2 on Cu ( 111), (100), and (110) surfaces, it was found that CO 2 molecules aligned parallel to Cu ( 111) and ( 100), whereas a vertical configuration was more stable for the adsorbed CO 2 on Cu (110) with one of two oxygen atoms towards the surface.…”

“…The presence of preadsorbed oxygen was responsible for forming carbonates of different structures [87,93]. On most metal surfaces, CO 2 activation is highly surface orientated, pressure-and particle size-dependent [89,[94][95][96]. Yu et al [96] demonstrated through spin-polarized DFT calculations that adsorption and dissociation of CO 2 was dependent on the Co particle size.…”

Revealing the Surface Chemistry for CO2 Hydrogenation on Cu/CeO2–x Using Near-Ambient-Pressure X-ray Photoelectron Spectroscopy

“…However, theoretical calculations proved that formate is a reactive intermediate for CO 2 conversion to methanol, rather than a spectator, even though it accumulates on the Cu/ZrO 2 surface . Furthermore, DRIFTS, IRRAS, and NAP-XPS studies and theoretical calculations also showed that the activation barrier for the rate-limiting step in the carbonate, formate, and carbonyl pathways is dependent on the catalysts, and the Cu/CeO 2– x interface can lower the activation barrier for the formate pathway. ,,,− Thus, in our NAP-XPS study, the RWGS route on the Cu/CeO 2– x surface via CO 2 dissociation in the form of carbonate, the conversion of carbonate to formate, and the decomposition of formate to CO becomes feasible.…”

Inducing High-Energy-Barrier Tribochemical Reaction Pathways; Acetic Acid Decomposition on Copper

“…Here, shear causes one of the carboxylate oxygens to detach from the surface to initially form an η 1 -acetate species that continues to tilt as the reaction proceeds. This induces the formation of a bent CO 2 δ− species that has been detected on copper at high CO 2 pressures [45,46], which reacts to form CO and adsorbed oxygen.…”

“…This suggests an alternative possibility that large stresses parallel to the plane of the adsorbed acetate induces the formation of monodentate acetate species, which then decomposes to form CO and adsorbed oxygen (Fig. 7) via a bent CO 2 δ− intermediate [45,46]. The reaction also deposits methyl species onto the copper surface so that one of the main differences between the thermal and mechanochemical processes is the temperature at which the resulting methyl species are deposited on the surface, where they are formed thermally at ~ 590 K, but tribochemically at ~ 300 K. This will likely influence the subsequent reactions of the products.…”