Carbon Dioxide Adsorption on V2O3(0001)

Abstract

oxidation, selective reduction, and dehydrogenation of hydrocarbons and other organic compounds [1,2]. Examples are sulfuric acid production and the oxidation of butane to maleic anhydride [3]. The manifold of catalytic applications has triggered numerous fundamental research studies of vanadium oxides aiming to improve the microscopic understanding of the catalytic processes. A complete overview of the present state of the research cannot be given here; the reader is referred to the literature. Some aspects are summed up in recent review papers [2,[4][5][6][7][8][9]. Catalysts involving vanadium oxides are usually based on V 2 O 5 , which contains vanadium in its highest oxidation state +5, but under reaction conditions the oxidation state may be lower. Therefore the corundum type oxide V 2 O 3 has also been the topic of a number of studies (for an overview, see [2,9]). These studies benefited from the fact that V 2 O 3 layers with (0001) orientation can easily be grown on Au(111), Pd(111), Cu 3 Au(100) and W(110) [2,[9][10][11][12]. Adsorption studies have been performed for methanol [13,14], water [15,16], and O 2 [17]. The surface structure is a critical parameter for the reactivity of a material and therefore the structure of the V 2 O 3 (0001) surface has been investigated thoroughly. Guided mainly by the presence of an intense vanadyl induced feature in vibrational spectra [10,11] is was concluded that the surface should be terminated by a layer of vanadyl groups. This was questioned some years ago by studies which reported that the surface should be terminated by a quasi-hexagonal oxygen layer [18][19][20]. A later I/V-LEED (LEED = low energy electron diffraction; I/V-LEED = LEED intensity analysis) study could show that the initial picture of a vanadyl terminated surface is probably correct [21,22] and therefore we will use the term 'vanadyl terminated' throughout this text. The vanadyl terminated V 2 O 3 (0001) surface can be reduced by electron bombardment such that the oxygen atoms of the vanadyl Abstract The adsorption of carbon dioxide on epitaxially grown V 2 O 3 layers on Au(111) has been studied with thermal desorption and infrared absorption spectroscopy. It is shown that the as-grown grown oxide layer does not react with carbon dioxide; the molecule binds weakly to the surface, stays intact and desorbs below 200 K. If the oxide is weakly reduced such that part or all of the oxygen atoms of the surface vanadyl layer is removed, then a surface carboxylate, i.e. CO − 2 bound to surface vanadium is formed. Part of the CO 2 derived species decompose into O+CO upon annealing, with the oxygen atoms re-oxidizing the reduced oxide surface.

CO2-Assisted Oxidative Dehydrogenation of Propane over VOx/In2O3 Catalysts: Interplay between Redox Property and Acid–Base Interactions

“…53−55 The negative bands are indicative of the CO 2 adsorption on vanadyl groups. 56 In sum, adding VO x significantly neutralizes the surface basicity of In 2 O 3 . Together with the retarded reduction of In 2 O 3 , the presence of VO x might explain the suppressed PDR pathway.…”

Surface Action Spectroscopy: A Review and a Perspective on a New Technique to Study Vibrations at Surfaces

“…Curve a) displays the IRAS spectrum which was obtained via dividing the sample spectrum by a reference spectrum: the sample spectrum was taken from the V 2 O 3 (0001)/Au(111) with a full coverage of vanadyl groups, while the reference spectrum was taken from a V 2 O 3 (0001)/Au(111) film where the surface vanadyl groups were removed by electron bombardment [63] . This vanadyl free, reduced film is quite reactive and able to extract oxygen from CO 2 in the background to form isolated V=O groups on the surface, as we know from infrared spectroscopy [64] . The vibration of such isolated V=O groups has a lower energy than 1040 cm −1 due to the reduced dipole coupling between V=O groups, [64] leading to the peak at 1008 cm −1 in the action spectrum.…”

“…[63] This vanadyl free, reduced film is quite reactive and able to extract oxygen from CO 2 in the background to form isolated V=O groups on the surface, as we know from infrared spectroscopy. [64] The vibration of such isolated V=O groups has a lower energy than 1040 cm À 1 due to the reduced dipole coupling between V=O groups, [64] leading to the peak at 1008 cm À 1 in the action spectrum. Therefore, when the sample IRAS spectrum is divided by the reference spectrum, a negative peak shows up, related to the V=O vibration mode of isolated vanadyl groups at 1008 cm À 1 as detected in the surface action spectroscopy.…”

Surface action spectroscopy with rare gas messenger atoms

“…If the differences between sample and reference sample are localized in the surface region, then all bulk-related intensity is removed by the division procedure. Electron irradiation leads to an ordered surface without vanadyl groups 44 , but the reduced, vanadyl free surface is very reactive and via reaction with carbon dioxide in the residual gas atmosphere new vanadyl groups are formed 45 . The vibrational energy of these newly formed vanadyl groups is lower due to the lower density of these groups and the consequently reduced dipole coupling.…”