Characterization of WOx/CeO2 catalysts and their reactivity in the isomerization of hexane

Mamede, Anne-Sophie; Payen, Edmond; Grange, Paul; Poncelet, Georges; Ion, Ana; Alifanti, M.; Parvulescu, VI

doi:10.1016/j.jcat.2004.01.008

Cited by 115 publications

(51 citation statements)

References 39 publications

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“…The characteristic feature of the Ce3d spectrum of Ce 4+ is the existence of a high BE satellite at ~916 eV (Mamede, et al, 2004;Hashimoto, et al, 1997), which is absent from the Ce3d spectrum of Ce 3+ (Hashimoto, et al, 1997). In our case, the satellite was absent from the Ce3d spectrum recorded for Ce4 (Figure 2), and, therefore, there was only Ce 3+ and no Ce 4+ .…”

Section: Al-ce Vermiculitesmentioning

confidence: 39%

Characterization of Al-Zr, Al-Hf and Al-Ce-pillared vermiculites by X-ray photoelectron spectroscopy

Campos

Moreno

Molina

2014

Rev. Acad. Colomb. Cienc. Ex. Fis. Nat.

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X-ray photoelectron spectroscopy was used to establish the relative concentration and the chemical environment of modifying species in a series of vermiculites pillared with mixed precursors of Al-Zr, Al-Hf and Al-Ce. The binding energies observed provided evidence that zirconium and hafnium are most likely found as Zr-O(H)-and/or Zr-Siand HfO 2 , displaying a larger dispersion on the vermiculite surface compared with cerium species (Ce 2 O 3 ), which are mainly found inside clay aggregates. On the one hand, the chemical analysis showed that with Al-Hf and Al-Zr solutions, the introduction of hafnium and zirconium was complete within the range of 0.5 -2 mmol g -1 of clay, but the efficiency was reduced with larger quantities. On the other hand, the introduction of cerium in the Al-Ce solutions can be considered to be complete within the range assessed.Key words: Pillared vermiculite, zirconium, hafnium, cerium, XPS. Caracterización de vermiculitas pilarizadas con Al-Zr, Al-Hf y Al-Ce por espectroscopía de fotoelectrones emitidos por rayos-X ResumenSe utilizó la espectroscopia de fotoelectrones emitidos por rayos-X para establecer la concentración relativa y el ambiente químico de las especies introducidas en una serie de vermiculitas pilarizadas con precursores mixtos de AlZr, Al-Hf y Al-Ce. Las energías de enlace observadas evidenciaron que es más probable encontrar zirconio y hafnio como Zr-O(H) -o Zr-Si-y HfO 2 , y que estos exhiben, además, una mayor dispersión en la superficie de la vermiculita en comparación con las especies de cerio (Ce 2 O 3 ), las cuales se encuentran principalmente en el interior de las láminas de arcilla. Por un lado, el análisis químico mostró que con las soluciones de Al-Hf y Al-Zr, la introducción de hafnio y de zirconio era completa dentro del rango de 0,5 a 2 mmol g -1 de arcilla, pero que la eficacia se reducía con cantidades más grandes. Por otro lado, la introducción de cerio en las soluciones de Al-Ce pudo considerarse completa dentro del rango evaluado.Palabras clave: vermiculita pilarizada, zirconio, hafnio, cerio, XPS.

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Section: Al-ce Vermiculitesmentioning

confidence: 39%

Characterization of Al-Zr, Al-Hf and Al-Ce-pillared vermiculites by X-ray photoelectron spectroscopy

Campos

Moreno

Molina

2014

Rev. Acad. Colomb. Cienc. Ex. Fis. Nat.

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“…Anyway the decay was also higher for these catalysts, and after 1 h the differences among the two series were quite small. As it was previously reported 22 the influence of the W content was different for the two series of catalysts, high W content corresponding to the most active for the P-series, and less W content for the I-series.…”

Section: Catalytic Activitysupporting

confidence: 58%

“…This change in the selectivity is quite unusual since we have demonstrated in the previous paper 22 that the reaction to methylcyclopentane goes through hexene intermediates, and the dehydrogenation of hexane to hexenes is thermodinamically favoured by the increase of the temperature. Actually, as it will be shown further, the decrease in the selectivity to methylcyclopentane corresponded to the increase of the coke content, which is evidence that the formation of coke involves, at least in the first step, the same intermediates.…”

Section: Catalytic Activitymentioning

confidence: 75%

“…The Raman spectrum of 15% WO x /CeO 2 catalyst (Figure 19a) exhibits an intense line at 462 cm 21 that is characteristic of crystalline CeO 2 and also two sharp lines at 924 and 942 cm 21 assigned to well crystallized Ce 2 (WO 4 ) 3 . 22 Moreover, we can exclude the formation of WO 3 whose major Raman line is expected at 806 cm 21 . During the pre-treatment under hydrogen and also during the reaction mixture under hexane/H 2 , no change occurred in the region of the polytungstate species lines (Figure 19b).…”

Section: Analysis Of the Coke Depositionmentioning

confidence: 98%

“…We have demonstrated that in combination with tungsten it leads to active catalysts in isomerization of hexane. 22 The presence of CeO 2 enhances the oxidative properties of the support, favoring the activation of alkenes via a hydrogen subtraction. These hexenes can isomerize on the catalysts acid sites, or they can follow the mechanism of the reaction described by the left part in the Scheme 1.…”

Section: General Assessmentsmentioning

confidence: 99%

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WO_x‐CeO₂ and WO_x‐Nb₂O₅ catalysts deactivation during hexane isomerization

Mamede¹,

Payen²,

Granger³

et al. 2008

AIChE Journal

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in Wiley InterScience (www.interscience.wiley.com).Two series of WO x -CeO 2 catalysts containing 10, 12, and 15 wt % W were prepared by co-precipitation and incipient wetness impregnation using a reported procedure. WO x -Nb 2 O 5 catalysts with the same amount of W were prepared by co-precipitation starting from an aqueous solution of ammonium niobium oxalate and ammonium metatungstate with ammonia, until reaching pH 7. After calcining for 3 h in static air at 973 K, the deactivation of the catalysts was investigated using isomerization of hexane as probe reaction at temperatures in the range 393-513 K, both in the absence and in the presence of hydrogen. In-situ Raman spectra during deactivation were recorded as well. The deactivation rate was fitted by an empirical Voorhies equation: R 5 m t 2n , where the values of n correlated very well with the mass loss determined from TG analysis.

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XRD–Raman and Modulation Excitation Spectroscopy

Beek¹,

Urakawa²,

Milanesio³

2013

In‐situ Characterization of Heterogeneous Catalysts

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Characterization of WOx/CeO2 catalysts and their reactivity in the isomerization of hexane

Cited by 115 publications

References 39 publications

Characterization of Al-Zr, Al-Hf and Al-Ce-pillared vermiculites by X-ray photoelectron spectroscopy

Characterization of Al-Zr, Al-Hf and Al-Ce-pillared vermiculites by X-ray photoelectron spectroscopy

WO_x‐CeO₂ and WO_x‐Nb₂O₅ catalysts deactivation during hexane isomerization

XRD–Raman and Modulation Excitation Spectroscopy

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Characterization of WOx/CeO2 catalysts and their reactivity in the isomerization of hexane

Cited by 115 publications

References 39 publications

Characterization of Al-Zr, Al-Hf and Al-Ce-pillared vermiculites by X-ray photoelectron spectroscopy

Characterization of Al-Zr, Al-Hf and Al-Ce-pillared vermiculites by X-ray photoelectron spectroscopy

WOx‐CeO2 and WOx‐Nb2O5 catalysts deactivation during hexane isomerization

XRD–Raman and Modulation Excitation Spectroscopy

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WO_x‐CeO₂ and WO_x‐Nb₂O₅ catalysts deactivation during hexane isomerization