Studies of molybdena-alumina catalysts

Liu, H.-c.; Weller, Sol W.

doi:10.1016/0021-9517(80)90008-1

Cited by 43 publications

(2 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Analogously, it is possible that the photoreduction during XPS measurement may also affect the structure of the surface vanadate species: It has been reported in the earlier literature that supported Mo and V species aggregate upon reduction in hydrogen. ,,, Therefore, IS spectra were taken also from samples that had not been exposed to X-rays before. During the extended XPS measurements documented in Figure , no significant changes were noted in the V-support ion atomic ratios.…”

Section: Resultsmentioning

confidence: 99%

Surface-Analytical Studies of Supported Vanadium Oxide Monolayer Catalysts

et al. 2004

View full text Add to dashboard Cite

Supported vanadium oxide catalysts, consisting of surface vanadia species on Al2O3, ZrO2, CeO2, and Nb2O5 oxide supports, were investigated by X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) to elucidate the effect of calcination treatments as well as exposures to (nonmonochromatized) X-rays and He ions on the surface properties. It was found that calcination in air at 730 K of samples that had been previously calcined in air at 773 K and exposed to ambient atmosphere results in significant increases of the V intensity relative to the support signal both in XPS and ISS. This indicates that the surface vanadia species aggregate under the influence of moisture, but spread during calcination. The surface V(V) species were reduced to V(IV) upon extended exposure to X-rays of a nonmonochromatized source, which was accompanied by clustering as detected by ISS. Following a new methodology that avoids these effects by studying freshly calcined samples transferred without exposure to ambient atmosphere, without previous illumination by X-rays, and takes account of the abrasive effect of He ions by extrapolating the results of sputter series, it was found that in supported V2O5/ZrO2, V2O5/CeO2, and V2O5/Nb2O5 catalysts possessing a vanadia monolayer coverage or above, the supports are densely covered by two-dimensional surface vanadia species, and the underlying oxide support cations of Zr, Ce, or Nb are not exposed. For a supported V2O5/Al2O3 catalyst containing a monolayer surface coverage of vanadia, however, a slight exposure of the oxide support cation (Al3+) was noted, which may originate from the much higher surface area of this support (Al2O3 ≫ Nb2O5, ZrO2, and CeO2) resulting in a higher curvature of the surfaces covered by the supported vanadia species. The current XPS and ISS surface studies confirm that supported vanadium oxide catalysts consist of close-packed monolayers of surface vanadia species.

show abstract

Section: Resultsmentioning

confidence: 99%

Surface-Analytical Studies of Supported Vanadium Oxide Monolayer Catalysts

et al. 2004

View full text Add to dashboard Cite

show abstract

“…Tungsten Uptake. The tungsten surface concentration (W/atoms nm -2 ) was calculated from the analytical tungsten content and surface area values after correction for the W content …”

Section: Resultsmentioning

confidence: 99%

Characterization of the Zirconia-Supported Tungsten Oxide System by Laser Raman and Diffuse Reflectance Spectroscopies

Gazzoli¹,

Valigi²,

Dragone³

et al. 1997

J. Phys. Chem. B

View full text Add to dashboard Cite

Zirconia-supported tungsten oxide samples, prepared by the equilibrium adsorption method in the pH range 2−13 by using as a support either hydrous [ZrO2(383)] or thermally pretreated [ZrO2(T)] zirconium oxide, were studied by laser Raman and diffuse reflectance spectroscopies. The W uptake increased (from ∼1.0 to ∼2.8 atoms nm-2) as the pH decreased for the ZrO2(T) supports, whereas for hydrous zirconia support showed the opposite trend. Different tungsten species were revealed depending on the amount of the adsorbed tungsten but not on the pH of the contacting solution. The continuous frequency shift of the Raman bands with the tungsten content, from 930 to 975 cm-1, indicated the presence of monomeric species at low tungsten concentrations and of polymeric species at high loading. The uptake of the tungsten species depends on the morphology and the texture of the support.

show abstract

Methodical aspects in the surface analysis of supported molybdena catalysts

Briand

Ткаченко

Guraya

et al. 2004

Surface & Interface Analysis

View full text Add to dashboard Cite

Supported molybdena catalysts, with TiO 2 , CeO 2 and Al 2 O 3 supports, were studied by XPS and ISS. It was found that reliable results are obtained only when samples are calcined and transferred into the ultrahigh vacuum system without further contact with the ambient atmosphere ('in situ calcination'). This applies also to catalysts that were previously calcined but had been stored in the ambient atmosphere.

show abstract

Studies of molybdena-alumina catalysts

Cited by 43 publications

References 13 publications

Surface-Analytical Studies of Supported Vanadium Oxide Monolayer Catalysts

Surface-Analytical Studies of Supported Vanadium Oxide Monolayer Catalysts

Characterization of the Zirconia-Supported Tungsten Oxide System by Laser Raman and Diffuse Reflectance Spectroscopies

Methodical aspects in the surface analysis of supported molybdena catalysts

Contact Info

Product

Resources

About