Vanadium oxide surfaces and supported vanadium oxide nanoparticles

Abstract

The information obtained from the characterization of vanadium oxide single crystal surfaces is related to the study of vanadia nanoparticles supported on silica and alumina thin films, model systems for the so-called “supported monolayer vanadia catalysts”. It is found that these particles have properties similar to V2O3 surfaces, where the topmost V ions are involved in vanadyl groups and have a 5+ oxidation state. A vibrational spectroscopy investigation combined with DFT calculations show that the accepted interpretation of vibrational spectra from vanadia catalysts must be revised

Selectivity in Methanol Oxidation as Studied on Model Systems Involving Vanadium Oxides

“…However, if the surface is reduced the situation changes considerably. We note that, different from Cr 2 O 3 (0001) [28], where we encountered a similar structural situation, the vanadyl groups cannot be reduced thermally without destroying the surface structure [16,19]. In fact, it is necessary to electron bombard the surface to selectively remove the vanadyl oxygen atoms as shown in Fig.…”

“…The final result of a V 2 O 3 (0001) surface shows in Fig. 1c the typical hexagonal lattice of protrusions of a depolarized corundum type (0001) surface, which is expected to be terminated by half a metal ion layer with exactly the exposed surface unit cell, if the surface structure is directly derived from a cut through the bulk structure in between the puckered vanadium ion layers [16]. This situation is depicted in Fig.…”

“…1d. It will become clear further below in this paper that the surface is, in fact, not terminated in this way but rather by a layer of V=O (vanadyl) bonds with the same registry [16]. Before we discuss the evidence for this we present details for the first steps of the processes involved in the transformation from V 2 O 5 (001) towards V 6 O 13 and V 2 O 3 respectively.…”

“…[8][9][10][11] and the synthesis of the thin vanadia films has been detailed in Ref. [16,19]. The V 2 O 3 films have been either used as prepared or they have been reduced by electron bombardment before exposure to the alcohol.…”

“…To obtain a more direct insight into structure-reactivity relations supported vanadia systems have been prepared under ultrahigh vacuum conditions on silica, alumina, and ceria thin film supports [8][9][10][11][12][13][14][15][16]. Scanning tunneling microscopy has been used to show that under such conditions the vanadia does not wet the surfaces of silica and alumina even if those surfaces had been exposed to water beforehand.…”