Carbon Dioxide Adsorption on V₂O₃(0001)

The adsorption of carbon dioxide on epitaxially grown V2O3 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. CO̅2 bound to surface vanadium is formed. Part of the CO2 derived species decompose into O+CO upon annealing, with the oxygen atoms re-oxidizing the reduced oxide surface

X-ray spectroscopic fingerprints of reactive oxygen sites at the MoO3(0 1 0) surface

The identification of oxygen sites at metal oxide surfaces and the characterization of their properties is of great importance for an understanding of the catalytic activity of such materials and, thus, for a rational design of efficient and selective catalysts. In the case of the clean MoO3(0 1 0) surface we show that an unambiguous discrimination of the different reactive oxygen sites can be obtained by angle-resolved near-edge X-ray absorption fine structure (NEXAFS) combined with density functional theory (DFT) based spectrum analyses for different photon polarization directions. In particular, we are able to unequivocally discriminate the characteristic spectral signatures of singly coordinated molybdenyl oxygen covering the topmost molybdenum layers from those of other oxygen centers that have very similar local environment and only differ by their spatial orientation in the crystal. Theoretical predictions are also successfully used to identify and interpret characteristic features in the NEXAFS spectra that arise from specific vacancy sites present at oxygen deficient surfaces

Well-ordered molybdenum oxide layers on Au(111): Preparation and properties

MoO3 layers on Au(111) were prepared via oxidation of molybdenum at elevated temperature in an atmosphere of 50 mbar of O2. Three different types of oxide structures were identified. Up to monolayer oxide coverage a structure with a c(4 × 2) unit cell relative to the Au(111) unit cell forms. This structure was previously identified as being similar to a monolayer of α-MoO3.(1) At larger coverages of up to two layers an oxide with a 11.6 Å × 5 Å rectangular unit cell appears. Further increase in the coverage leads to the occurrence of crystallites of regular α-MoO3 with a very small density of defects. These crystallites grow with the (010) plane parallel to the substrate surface and with random azimuthal orientation leading to rings in the LEED pattern. With increasing layer thickness the crystallites start to coalesce until finally a closed film forms. These layers sublimate at temperatures between about 670 and 770 K with the MoO3 aggregates sublimating at lower temperature than the bilayer and monolayer films. © 2013 American Chemical Society