Solid Solutions of WO3into Zirconia in WO3–ZrO2 Catalysts

Cortés-Jácome, M.A.; Toledo-Antonio, J.A.; Armendáriz, H.; Hernández, I.; Bokhimi, X.

doi:10.1006/jssc.2001.9488

Cited by 21 publications

(18 citation statements)

References 21 publications

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“…It is hypothesized [29,30] that the entrapment of tungstate ions by zirconium hydroxide during precipitation results in an intimate interaction between WO 4 2-and zirconia in calcined catalysts. This hypothesis was supported by Cortes-Jacome et al [31][32][33]. Their results are consistent with the formation of solid solutions Zr 1-x W x O 2?x/2 in calcined coprecipitated WO 4 2-/ZrO 2 samples.…”

Section: Introductionsupporting

confidence: 90%

Bulk and surface characterization and isomerization activity of Pt/WO4 2−/ZrO2 catalysts of different preparations

Kuznetsov

Kazbanova

Кузнецова

et al. 2014

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The texture, phase and surface composition and acidity of impregnated and precipitated Pt/WO 4 2-/ZrO 2 catalysts have been investigated with XRD, XPS, FTIR spectroscopy, and BET measurements. It has been shown that increasing the tungstate ion concentration in hydrated zirconium oxide results in an increase in the t-ZrO 2 fraction in the catalysts following high temperature activation. While a fraction of W 6? and W 5? cations forms a solid solution with zirconia, the remaining W ions are stabilized on the catalysts surface as (-WO x -) n clusters. The catalytic activity in n-heptane isomerization seems to correlate with catalyst surface acidity to reach the greatest value at the WO 4 2-concentration in the range of 12.9-17.6 mol %.

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Section: Introductionsupporting

confidence: 90%

Bulk and surface characterization and isomerization activity of Pt/WO4 2−/ZrO2 catalysts of different preparations

Kuznetsov

Kazbanova

Кузнецова

et al. 2014

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“…The increment of tungsten loadings resulted in the formation of WO 6 species on the catalyst surface. Cortes-Jacome et al prepared a WO x -ZrO 2 solid solution (14.6 wt% as WO 3 ) by calcination of the hydrogel at 833 K. 39,40 They propose that W 5C ions coexisting with W 6C species stabilize the tetragonal phase of zirconia, but tungsten atoms near the crystallite surface are oxidized to W 6C by calcination at 1073 K, causing the segregation of the tungsten species to form WO 3 nano-crystallites, followed by phase transformation to the monoclinic phase. 40 We presume these phenomena reported by Cortes-Jacome are consistent with a phase diagram of WO 3 -ZrO 2 system 36 because the calcination temperature of 833 K was considered to be insufficient to reach the thermodynamically equilibrium.…”

Section: Structure Of Tungsten Species In Wo X -Zromentioning

confidence: 99%

Structural analysis of tungsten–zirconium oxide catalyst by W K‐edge and L₁‐edge XAFS

2008

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The local structure of tungsten species in tungsten-zirconium-oxide catalysts (WO x -ZrO 2 ) was first investigated by W K-edge x-ray absorption spectroscopic techniques. A proportion of WO 4 to the total WO x species was quantitatively analyzed with W L 1 -edge x-ray absorption near edge structure (XANES). Tungsten species in 15 wt% WO x -ZrO 2 , which is the most active for n-butane skeletal isomerization, consists of a mixture of WO 3 -ZrO 2 solid solution, WO 6 aggregate and WO 4 species on the catalyst surface. The tungsten species does not possess long-range ordering.

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“…A detailed analysis of the structural and local order evolution of the zirconia tetragonal phase was followed by Rietveld refinement. 6 TEM images obtained in the sample annealed at 560°C showed big crystallites of about 50 nm, as observed in Fig. 2(a).…”

mentioning

confidence: 66%

“…WO x -ZrO 2 samples were prepared by precipitation method as was reported previously. 6 An aqueous 0.007 M solution of zirconia oxynitrate, ZrO(NO 3 ) 2 и6H 2 O (99%, Aldrich, Milwaukee, WI) and ammonium metatungstate hydrate, (NH 4 ) 6 W 12 O 39 иxH 2 O (99%, Aldrich) solution 0.007 M was precipitated at pH ‫ס‬ 9.5 to 10 with a solution of ammonium hydroxide 14 vol% NH 4 OH. The obtained white slurry was aged for 24 h at room temperature.…”

mentioning

confidence: 99%

Structural evolution of WO₃ nanoclusters on ZrO₂

et al. 2006

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Direct evidence of the transformation of WO x species in WO 3 nanoclusters on WO x -ZrO 2 system was achieved by high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy on samples obtained by a conventional precipitation method and annealed from 560 to 800°C. WO 3 Nanoclusters with 2-nm crystal size orthorhombic structure were identified on the ZrO 2 surface after annealing at 800°C.Tungsten oxide dispersed on zirconia in WO 3 -ZrO 2 system is one of the more stable mixed oxides with strongly acidic properties, which are of interest in catalytic processes. 1,2 The high acid site density has been explained by assuming that zirconia crystallites are covered with a WO x monolayer. 3-5 However, direct evidence of the structure and nature of these species on the ZrO 2 surface is scarce. In this work, experimental evidence of the growth of WO x species incorporated into the tetragonal zirconia phase into well-dispersed WO 3 nanoclusters on ZrO 2 surface was obtained by high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. WO x -ZrO 2 samples were prepared by precipitation method as was reported previously. 6 An aqueous 0.007 M solution of zirconia oxynitrate, ZrO(NO 3 ) 2 и6H 2 O (99%, Aldrich, Milwaukee, WI) and ammonium metatungstate hydrate, (NH 4 ) 6 W 12 O 39 иxH 2 O (99%, Aldrich) solution 0.007 M was precipitated at pH ‫ס‬ 9.5 to 10 with a solution of ammonium hydroxide 14 vol% NH 4 OH. The obtained white slurry was aged for 24 h at room temperature. The obtained gel was dried at 110°C for 18 h. The dried powders were annealed at 560, 700, and 800°C for 4 h in air flow. Bulk tungsten content was 11.6 wt% determined by atomic absorption spectroscopy in the sample after annealing at 800°C. The x-ray diffraction (XRD) patterns were recorded at room temperature with Cu K ␣ radiation in a Bruker Advance D-8 diffractometer (Karlsruhe, Germany). High-resolution (HR) transmission electron microscopy (TEM) images were performed in a field emission gun (FEG) JEOL 2010F (Tokyo, Japan) transmission electron microscope operating at 200 kV and chemical analysis by x-ray energy dispersive spectroscopy (EDX) was performed in a TEM Tecnai F30 Super Twin (Eindhoven, Netherlands). The Raman spectra were recorded at room temperature using a Jobin Yvon Horiba spectrometer (T64000, Lille, France), equipped with a confocal microscope (Olympus, BX41, Lille, France) with a laser 514.5 nm at a power level of 30 mW. The spectrometer is equipped with a charge-coupled detector (CCD).XRD patterns showed tetragonal phase for the samples calcined at 560 and 700°C, while tetragonal and monoclinic zirconia phases were detected when the samples were calcined at 800°C, as observed in Fig. 1. In addition, a small amount of WO 3 orthorhombic phase was segregated. A detailed analysis of the structural and local order evolution of the zirconia tetragonal phase was followed by Rietveld refinement. 6 TEM images obtained in the sample annealed at 560°C showed big crystallites of about 50 nm, as observed ...

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Solid Solutions of WO3into Zirconia in WO3–ZrO2 Catalysts

Cited by 21 publications

References 21 publications

Bulk and surface characterization and isomerization activity of Pt/WO4 2−/ZrO2 catalysts of different preparations

Bulk and surface characterization and isomerization activity of Pt/WO4 2−/ZrO2 catalysts of different preparations

Structural analysis of tungsten–zirconium oxide catalyst by W K‐edge and L₁‐edge XAFS

Structural evolution of WO₃ nanoclusters on ZrO₂

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Solid Solutions of WO3into Zirconia in WO3–ZrO2 Catalysts

Cited by 21 publications

References 21 publications

Bulk and surface characterization and isomerization activity of Pt/WO4 2−/ZrO2 catalysts of different preparations

Bulk and surface characterization and isomerization activity of Pt/WO4 2−/ZrO2 catalysts of different preparations

Structural analysis of tungsten–zirconium oxide catalyst by W K‐edge and L1‐edge XAFS

Structural evolution of WO3 nanoclusters on ZrO2

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Structural analysis of tungsten–zirconium oxide catalyst by W K‐edge and L₁‐edge XAFS

Structural evolution of WO₃ nanoclusters on ZrO₂