Characterization of tungsta-titania catalysts

A set of polycrystalline TiO 2 photocatalysts loaded with various ions of transition metals (Co, Cr, Cu, Fe, Mo, V, and W) were prepared by using the wet impregnation method. The samples were characterized by using some bulk and surface techniques, namely X-ray diffraction, BET specific surface area determination, scanning electron microscopy, point of zero charge determination, and femtosecond pump-probe diffuse reflectance spectroscopy (PP-DRS). The samples were employed as catalysts for 4-nitrophenol photodegradation in aqueous suspension, used as a probe reaction. The characterization results have confirmed the difficulty to find a straightforward correlation between photoactivity and single specific properties of the powders. Diffuse reflectance measurements showed a slight shift in the band gap transition to longer wavelengths and an extension of the absorption in the visible region for almost all the doped samples. SEM observation and EDX measurements indicated a similar morphology for all the particles, and a not homogeneous distribution of the metal species onto the surface of catalyst particles. The impregnated samples revealed recombination rates always higher than that of bare TiO 2 . The photoactivity of TiO 2 was reduced by the presence of transition metal ions with the exception of W, which instead played a beneficial role. The results of femtosecond pumpprobe diffuse reflectance spectroscopy appear quite in accord with the observed photocatalytic activity only for the lowest values of electron-hole recombination rate of the samples.

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“…[57][58][59] By comparing the results obtained in previous studies [52][53][54][55] the following variation in surface acidity has been proposed:…”

Section: Discussionmentioning

confidence: 99%

Preparation of Polycrystalline TiO₂ Photocatalysts Impregnated with Various Transition Metal Ions: Characterization and Photocatalytic Activity for the Degradation of 4-Nitrophenol

et al. 2001

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“…1), Raman spectra show the presence of a band between 950 and 975 cm À1 characteristic of surface W species [19,20,[29][30][31] and attributed to the vibration of W O bond in hydrated mono-oxotungstate species on titania surface [18,31]. No bands indicative of the presence of bulk WO 3 (bands at 806 and 713 cm À1 ) were detected.…”

Section: Raman Spectroscopymentioning

confidence: 96%

“…Towards this objective, the surface structure and catalytic properties of titania-supported W and Nb systems will be examined. These systems have also been shown to exhibit acidic properties [5,10,11,[16][17][18][19][20][21]. Characterization of both systems will be conducted by X-ray diffraction and Raman spectroscopy studies.…”

Section: Introductionmentioning

confidence: 99%

Acidity of titania-supported tungsten or niobium oxide catalystsCorrelation with catalytic activity

Onfroy

Clet

Bukallah

et al. 2006

Applied Catalysis A: General

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The acidity of catalytic systems based on tungsten oxide or niobium oxide supported on titania was compared. Two series with metal contents up to 3.6 atom nm À2 were prepared by incipient wetness impregnation of the titania support with ammonium metatungstate or niobium oxalate solutions. Characterization of both systems by X-ray diffraction and Raman spectroscopy studies did not show evidence of bulk metal oxide formation. The acidity was monitored by adsorption of 2,6-dimethylpyridine (2,6-lutidine) followed by infrared spectroscopy. The catalytic activity was tested for the reaction of isopropanol dehydration.At a reaction temperature of 403 K, WO x /TiO 2 catalysts were inactive for a surface density of W 1.2 W atom nm À2 . Above this loading, the activity increased progressively with increasing W content. Similar evolution was observed for the abundance of relatively strong Brønsted acid sites (i.e. able to retain lutidine at 573 K). In contrast, NbO x /TiO 2 catalysts were essentially inactive at this reaction temperature and a higher reaction temperature (473 K) was required to reach a comparable catalytic activity. No threshold of Nb loading for the development of catalytic activity was observed. Similar behavior was evidenced for the abundance of medium strength Brønsted acid sites (able to retain lutidine at 523 K). For both systems, a direct correlation between the catalytic activity and the abundance of Brønsted acid sites was observed. #

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“…6c, spectrum d) shows a band at 1012 cm -1 which gives a single W=O overtone vibration at 2012 cm -1 . These are the typical spectral features corresponding to surface monoxo W=O species [10,37]. The spectra of the dehydrated ion-exchanged samples in the 1050-950-cm -1 region (Fig.…”

Section: In Situ Ft-ir Spectroscopymentioning

confidence: 91%

Spectroscopic characterization of tungstated zirconia prepared by equilibrium adsorption from hydrogen peroxide solutions of tungsten(VI) precursors

Kantcheva

Koz

2007

J Mater Sci

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. The starting material is amorphous zirconium oxyhydroxide. The maximum W densities obtained are larger than that reported in the literature for systems synthesized by the same method using aqueous non-peroxide solutions. In the case of the metatungstate precursor, this increase is attributed to the generation of additional anchoring sites by interaction between the amorphous support and H 2 O 2 . The high uptake achieved when the peroxo complex is used as a precursor is a result of both the ZrO x (OH) 4-2x -H 2 O 2 interaction and low nuclearity of the adsorbing anion. The materials are characterized by XRD, DR-UV-vis, Micro-Raman and FT-IR spectroscopy. The surface acidities of samples with identical W loading prepared by equilibrium adsorption from the [H 2 W 12 O 40 ] 6--H 2 O 2 system and by impregnation with aqueous solution of ammonium metatungstate are investigated by FT-IR spectroscopy of CO adsorbed at 80 K.

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Characterization of tungsta-titania catalysts

Cited by 216 publications

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Preparation of Polycrystalline TiO₂ Photocatalysts Impregnated with Various Transition Metal Ions: Characterization and Photocatalytic Activity for the Degradation of 4-Nitrophenol

Preparation of Polycrystalline TiO₂ Photocatalysts Impregnated with Various Transition Metal Ions: Characterization and Photocatalytic Activity for the Degradation of 4-Nitrophenol

Acidity of titania-supported tungsten or niobium oxide catalystsCorrelation with catalytic activity

Spectroscopic characterization of tungstated zirconia prepared by equilibrium adsorption from hydrogen peroxide solutions of tungsten(VI) precursors

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Characterization of tungsta-titania catalysts

Cited by 216 publications

References 1 publication

Preparation of Polycrystalline TiO2 Photocatalysts Impregnated with Various Transition Metal Ions: Characterization and Photocatalytic Activity for the Degradation of 4-Nitrophenol

Preparation of Polycrystalline TiO2 Photocatalysts Impregnated with Various Transition Metal Ions: Characterization and Photocatalytic Activity for the Degradation of 4-Nitrophenol

Acidity of titania-supported tungsten or niobium oxide catalystsCorrelation with catalytic activity

Spectroscopic characterization of tungstated zirconia prepared by equilibrium adsorption from hydrogen peroxide solutions of tungsten(VI) precursors

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Preparation of Polycrystalline TiO₂ Photocatalysts Impregnated with Various Transition Metal Ions: Characterization and Photocatalytic Activity for the Degradation of 4-Nitrophenol

Preparation of Polycrystalline TiO₂ Photocatalysts Impregnated with Various Transition Metal Ions: Characterization and Photocatalytic Activity for the Degradation of 4-Nitrophenol