Adsorption and reaction of carbon dioxide on pure and alkali-metal promoted cold-deposited copper films
Introduction
Even in the early 1980s, the investigation of the chemistry of carbon dioxide was thought of as being of only minor importance, because the molecule was expected to be rather unreactive in the sense that in many cases the reactions had to overcome a rather high activation barrier 1, 2. However, by the introduction of a metal complex (e.g. in the form of a catalyst) this barrier can be reduced, going along with an increase in the reaction rate. However, only after the introduction of the so-called “ICI” process for methanol synthesis [3], and especially after the claim that carbon dioxide was the source of carbon in the reaction had been widely accepted, has the adsorption and activation of CO2 become object of intense research. Reviews of the current understanding of carbon dioxide chemistry have been published recently 4, 5.
Here we present our recent results of the investigation of carbon dioxide adsorption, activation and reaction on rough copper surfaces using surface enhanced Raman spectroscopy and X-ray photoelectron spectroscopy. The results have implications for the industrial methanol synthesis process, where methanol is produced by passing syngas (CO/CO2/H2) over a Cu/ZnO/Al2O3 catalyst. It seems that in this process the CO2 is the main source of carbon 6, 7, that at least the critical steps of the reaction take place on copper sites [8], and that the role of ZnO may be to maintain more of the metallic copper in the form of thin islands [9]. Special regard was directed in our experiments towards the reaction of carbon dioxide or its reaction products with coadsorbed hydrogen atoms to form an adsorbed formate species, because there is much evidence that formate is the pivotal intermediate in methanol synthesis [10].
The article is structured as follows: after an experimental section, the results of the investigations of the adsorption of carbon dioxide on clean and K-promoted copper are presented. The subsequent sections concern the coadsorption of carbon dioxide and atomic hydrogen on K-doped copper, and for comparison a discussion of synthesised formate adsorbed on clean and alkal-metal doped copper surfaces. The literature concerning these topics will be discussed in the relevant sections.
Section snippets
Experimental
The UHV chamber used in the experiments has been described previously [11]. Copper films were prepared in-situ by depositing the metal on to polished copper plates, which were cooled to a temperature TS of typically around 40 K. Depositing metals in this manner creates highly porous films with substantial amounts of atomic-scale defects 12, 13, 14. Doping of the alkali metal was performed using standard dispensers (SAES Getters). The amount of deposited copper as well as of the alkali metal was
CO2 adsorption on clean Cu
In its dependence on the substrate, carbon dioxide shows a rather complex adsorption behaviour. According to the crystallographic orientation and the properties of surface physisorption, chemisorption and even dissocation and reaction can occur.
At sufficiently low temperatures, CO2 is only weakly adsorbed on low-index copper surfaces in its molecular form. For Cu(100), a desorption temperature between 86 and 90 K has been found, depending on the surface coverage [22]. On cold-deposited copper
Summary
Surface enhanced Raman spectra of CO2 and HCOOH adsorbed on clean and alkali-metal doped copper surfaces have been presented. As well as activation, a reaction of the carbon dioxide to give carbonate and carbon monoxide has been observed on a potassium-doped cold-deposited copper surface. The experiments give no indication of possible intermediates in the reaction path. When coadsorbing CO2 and atomic H on such a substrate, the formation of a surface-bound formate species seems to occur when
Acknowledgements
This research was carried out as part of the project “Catalytic Chemistry of CO2 at Clean and Modified Metal, Oxide and Metal-Oxide Surfaces: a Surface Science Approach”, and was supported by the European Union (Contract No. BRE2.CT93.0448, Project No. 5027) and the Ministerium für Wissenschaft und Forschung des Landes Nordrhein–Westfalen. We have profited from discussions with A. Carley, H.-J. Freund, M.W. Roberts, M. Spencer and their co-workers. Special thanks are due to M. Faubel for
References (103)
J. Mol. Catal.
(1991)- et al.
Surf. Sci. Rep.
(1996) - et al.
Appl. Catal.
(1987) - et al.
Appl. Catal.
(1986) - et al.
J. Catal.
(1996) Surf. Sci.
(1995)J. Electron Spectrosc. Relat. Phenom.
(1976)- et al.
Surf. Sci.
(1992) - et al.
Surf. Sci.
(1987) - et al.
Surf. Sci.
(1996)
Surf. Sci.
Surf. Sci.
Appl. Surf. Sci.
Surf. Sci.
Surf. Sci.
Surf. Sci.
Surf. Sci.
Surf. Sci.
Surf. Sci.
Vacuum
Surf. Sci.
Surf. Sci.
Surf. Sci.
Surf. Sci.
Surf. Sci.
Surf. Sci.
Surf. Sci.
Surf. Sci.
Surf. Sci.
Solid State Commun.
Solid State Commun.
Surf. Sci.
Surf. Sci.
Chem. Phys. Lett.
Surf. Sci.
Surf. Sci.
Surf. Sci.
Surf. Sci.
Surf. Sci.
Surf. Sci.
Surf. Sci.
Surf. Sci.
Surf. Sci.
J. Electron Spectrosc. Relat. Phenom.
Surf. Sci.
Angew. Chem.
Chemtech
J. Chem. Soc., Faraday Trans. I
J. Raman Spectrosc.
Cited by (35)
Development and performance of CeO<inf>2</inf> supported BaCoO<inf>3−δ</inf> perovskite for chemical looping steam methane reforming
2023, Fuel Processing TechnologyCitation Excerpt :The peak at 1507 cm−1 was attributed to CH bending [56], the peak at 1473 cm−1 was assigned to the scissoring vibration of CH2 species [57]. The prominent peak at 1435 cm−1 was attributed to the symmetric and asymmetric methyl bends of the -O-CH3 species [58], and the absorption band at 1337 cm−1 was assigned symmetric stretch vibrations of carbonate species [46,59], The peaks at 1455 cm−1 and 1304 cm−1 were attributable to the deformation vibration of the CH bond in adsorbed methane and the asymmetric stretching vibration of the -CH3 species [47]. The absorption bands of methane and -CH3 decreased with the increase of temperature, suggesting that the conversion of methane was enhanced with the increase of reaction temperatures.
Facile fabrication of ultrathin freestanding nanoporous Cu and Cu-Ag films with high SERS sensitivity by dealloying Mg-Cu(Ag)-Gd metallic glasses
2021, Journal of Materials Science and TechnologyTwo-step fabrication of nanoporous copper films with tunable morphology for SERS application
2018, Applied Surface ScienceSurface chemistry of carbon dioxide revisited
2016, Surface Science ReportsCitation Excerpt :The K-doped, cold deposited Cu film demonstrated the formation of CO and carbonates, in addition to the other species existing on the surface of its clean counterpart. On this surface, bending mode and symmetric vibration of the bent CO2 exhibited peaks at 754 and 1197 cm−1, while those of the physisorbed CO2 molecule were detected at 640 and 1372 cm−1, respectively [115]. The reactivity of alkali metals towards CO2 resulted in the peaks detected at 280, 368, and 2055 cm−1, characteristics of liberation and frustrated translation, as well as stretching modes of carbon monoxide.
The influence of electron confinement, quantum size effects, and film morphology on the dispersion and the damping of plasmonic modes in Ag and Au thin films
2015, Progress in Surface ScienceCitation Excerpt :A key factor in relaxation processes is the lifetime of the SP, which is limited by the decay into e–h pairs (Landau damping [36,41,208]). The lifetime of SP strongly influences plasmon-mediated dynamic processes and, moreover, the field enhancement and the sensitivity of SERS [34,209–213] and surface-enhanced fluorescence [214–217]. Many SP polariton-based applications relie on SP lifetime.