Surface Chemistry of Cu in the Presence of CO₂ and H₂O

Abstract

The chemical nature of copper and copper oxide (Cu 2 O) surfaces in the presence of CO 2 and H 2 O at room temperature was investigated using ambient pressure x-ray photoelectron spectroscopy. The studies reveal that in the presence of 0.1 torr CO 2 several species form on the initially clean Cu, including carbonate CO 3 2 , CO 2 δ-and C 0 , while no modifications occur on an oxidized surface. The addition of 0.1 ML Zn to the Cu results in the complete conversion of CO 2 δ-to carbonate. In a mixture of 0.1 torr H 2 O and 0.1 torr CO 2 , new species are formed, including hydroxyl, formate and methoxy, with H 2 O providing the hydrogen needed for the formation of hydrogenated species.

Subsurface oxide plays a critical role in CO 2 activation by Cu(111) surfaces to form chemisorbed CO 2 , the first step in reduction of CO 2

“…(C) The adsorption of CO 2 when a subsurface oxide structure is deliberately incorporated into Cu(111) but without additional H 2 O. In this work we observe that a subsurface oxide coverage of about 0.08 ML is responsible for stabilizing l-CO 2 determining the initial species formed while exposed to realistic gas pressures of CO2 and H2O (13,15).…”

“…The deconvoluted C 1s spectra (see Supporting Information for further details) exhibit two main spectral regions: (i) At low BE we see chemical species that can be assigned as graphitic carbon (284.5 eV), sp 3 (C-C) carbon (285.2 eV), and C-O(H) bonds (286.3 eV), based on the literature values (15). (ii) At higher BE we see spectral fingerprints of higher oxidized carbon structures and adsorbed CO2, where deconvolution of the spectra indicates the presence of formate (HCOO−) (287.3 eV), chemisorbed (denoted b-CO2 for bent), and physisorbed CO2 (denoted l -CO2 for linear) (287.9 eV and 288.4 eV, respectively) and carbonate (−CO3) (289.4 eV) (15).…”

“…(ii) At higher BE we see spectral fingerprints of higher oxidized carbon structures and adsorbed CO2, where deconvolution of the spectra indicates the presence of formate (HCOO−) (287.3 eV), chemisorbed (denoted b-CO2 for bent), and physisorbed CO2 (denoted l -CO2 for linear) (287.9 eV and 288.4 eV, respectively) and carbonate (−CO3) (289.4 eV) (15). Finally, a sharp peak centered at about 293.3 eV corresponds to the photoelectron emission of g-CO2 (Fig.…”

Understanding complete oxidation of methane on spinel oxides at a molecular level

“…C-H vibrational peaks at 2,900-3,000 cm À 1 were identified during in situ studies of CH 4 combustion on NiCo 2 O 4 . They are contributed from C-H stretching of the spectator CH n species formed from dissociative adsorption of CH 4 , supported by the low C 1s binding energy of CH n (peak 1) at 285.9-284.8 eV (refs [25][26][27], and C-H stretching of the intermediate OCHO.…”

Photoelectron spectroscopy under ambient pressure and temperature conditions

“…This is an important result because it indicates that the measured water layer thickness corresponds to the equilibrium value with the vapor phase. The Cu-CO 2 -H 2 O system was studied recently by Xingyi et al 75 at the ALS beamline 11.0.2 using a polycrystalline foil that was cleaned in the preparation chamber described above. An evaporator in that chamber allowed also for the deposition of small amounts of Zn, an important ingredient in catalytic systems and also used in the motor brushes as a structural element.…”