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Journal ArticleDOI

WOx/ZrO2 catalysts: Part 1. Preparation, bulk and surface characterization☆

10 May 2002-Applied Catalysis A-general (Elsevier)-Vol. 231, Iss: 1, pp 159-172
TL;DR: In this paper, the surface area determination, X-ray diffraction, XRD, XPS, XAS, diffuse optical reflectance, Raman spectroscopy and chemical analysis of Zirconia supported tungsten oxide catalysts were performed.
Abstract: Zirconia supported tungsten oxide catalysts (tungsten content up to 337 wt%) were prepared by equilibrium adsorption and impregnation in acid (pH 27) and basic (pH 10) conditions using hydrous zirconium oxide After thermal treatment at 1073 K in air, the catalysts were characterized by surface area determination, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), diffuse optical reflectance, Raman spectroscopy and chemical analysis The results show that tungsten is present as a dispersed phase and as monoclinic WO3 crystallites The density of tungsten in a dispersed form was estimated as about 5 atoms nm−2 Leaching treatments with ammonia revealed that only a fraction of the dispersed tungsten interacts directly with the support surface The interacting species, in the form of small clusters, as revealed by EXAFS and Raman spectroscopy, control the ZrO2 surface area and are responsible for the structural changes in the support Subsequent thermal treatment up to 1073 K in air leaves them unchanged
Citations
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Journal ArticleDOI
TL;DR: In this article, the catalytic activity of the strong solid acid tungstated zirconia (WZ) was studied for the esterification of acetic acid and the transesterification of triacetin (a synthetic triglyceride in the liquid phase) with methanol.

240 citations

Journal ArticleDOI
TL;DR: In this article, an extensive series of supported WO3/ZrOx(OH)4−2x catalysts (WZrOH) were synthesized by standard aqueous impregnation of ammonium metatungstate into an amorphous Zr Ox(OH)/ZrO2 metastable support, followed by high-temperature calcination.

197 citations

Journal ArticleDOI
TL;DR: A series of supported WO 3 catalysts were synthesized by incipient wetness impregnation of ammonium metatungstate aqueous solutions onto Al 2 O 3, TiO 2, Nb 2 O 5, and ZrO 2 supports as a function of tungsten oxide loading.

168 citations

Journal ArticleDOI
TL;DR: High-angle annular dark-field imaging of WO(3)/ZrO(2) catalysts in an aberration-corrected analytical electron microscope allows, for the first time, direct imaging of the various species present and the deduction of the likely identity of the catalytic active site, subnanometre Zr-WO(x) clusters.
Abstract: Tungstated zirconia is a robust solid acid catalyst for light alkane (C4–C8) isomerization. Several structural models for catalytically active sites have been proposed, but the topic remains controversial, partly because of the absence of direct structural imaging information on the various supported WOx species. High-angle annular dark-field imaging of WO3/ZrO2 catalysts in an aberration-corrected analytical electron microscope allows, for the first time, direct imaging of the various species present. Comparison of the relative distribution of these WOx species in materials showing low and high catalytic activities has allowed the deduction of the likely identity of the catalytic active site—namely, subnanometre Zr–WOx clusters. This information has subsequently been used in the design of new catalysts, in which the activity of a poor catalyst has been increased by two orders of magnitude using a synthesis procedure that deliberately increases the number density of catalytically relevant active species. Small alkanes are typically isomerized on tungstated-alumina solid-acid catalysts, but the origin of the activity has been unclear. Now, high-resolution imaging has revealed subnanometre Zr-WOx clusters to be the active sites.

142 citations

Journal ArticleDOI
TL;DR: In this article, the esterification of palmitic acid with methanol was studied on zirconia supported tungsten oxide solid acid catalysts prepared by both impregnation and co-precipitation methods.
Abstract: Esterification of palmitic acid with methanol was studied on zirconia supported tungsten oxide solid acid catalysts prepared by both impregnation and co-precipitation methods; the tungsten loading and calcination temperature were varied. These catalysts were characterized by X-ray diffraction for structural elucidation and by temperature-programmed desorption of ammonia for their surface acidity. Whereas the impregnated catalysts exhibited both tetragonal and monoclinic phases of zirconia, at calcination temperatures beyond 500 °C their co-precipitated analogues showed stability towards the tetragonal phase. The formation of monoclinic phases of zirconia and crystalline tungsten oxide decreased the esterification activity, as a consequence of decreased surface acidity. Coexistence of tetragonal zirconia with the amorphous tungsten oxide offered maximum esterification activity.

134 citations

References
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Journal ArticleDOI
TL;DR: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations as mentioned in this paper.
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51,997 citations

Journal ArticleDOI
TL;DR: In this article, the results of photoelectric cross-sections for the Kα lines of magnesium at 1254 eV and of aluminum at 1487 eV were given for Z values up to 96.

4,891 citations

Journal ArticleDOI
M Boudart1

972 citations

Journal ArticleDOI
TL;DR: In this article, the infrared and Raman spectra of powder samples of WO3 (monoclinic and hexagonal) and XH 2 O (x = 1,2, 1 3 ) have been recorded and the most characteristic vibrations are discussed with reference to the available structural data.

856 citations