Structure–acidity correlation of supported tungsten(VI)-oxo-species: FT-IR and TPD studies of adsorbed pyridine and catalytic decomposition of 2-propanol

Zaki, Mohamed I.; Mekhemer, Gamal A. H.; Fouad, Nasr E.; Rabee, Abdallah I.M.

doi:10.1016/j.apsusc.2014.04.180

Cited by 16 publications

(7 citation statements)

References 26 publications

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“…Brønsted sites would be very strong on WO 3 /TiO 2 (still intense upon heating at 300 • C). The work of Zaki et al [87] clearly underlines the critical role of the support of tungsten oxides, both in the nature of W species and in their respective acidity.…”

Section: Silica-supported Tungsten Oxidesmentioning

confidence: 99%

“…Barton et al reported that supported tungsten oxide catalysts are able to generate Brønsted acid sites when W 6+ species are replaced by tungsten cations with lower valency [86]. A general overview of the acidity of tungstated oxides was performed by Zaki et al, who compared the relative strength of acid sites of 10% WO 3 samples deposited on Al 2 O 3 (69 m 2 g −1 ), TiO 2 (34 m 2 g −1 ) and SiO 2 (136 m 2 g −1 ) [87]. All samples were calcined at 500 • C. Well-dispersed monotungstates and polytungstates were the most abundant surface species on WO 3 /Al 2 O 3 , while 3D polytungstates were observed on WO 3 /TiO 2 .…”

Section: General Overviewmentioning

confidence: 99%

“…FTIR spectra of adsorbed pyridine at room temperature on Al 2 O 3 (Al), TiO 2 (Ti), SiO 2 (Si) and 10%WO 3 on these supports (code: WAl, WTi and WSi, respectively). From Zaki et al [87] with permission from Elsevier.…”

Section: Silica-supported Tungsten Oxidesmentioning

confidence: 99%

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Tungsten-Based Catalysts for Environmental Applications

2021

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This review aims to give a general overview of the recent use of tungsten-based catalysts for wide environmental applications, with first some useful background information about tungsten oxides. Tungsten oxide materials exhibit suitable behaviors for surface reactions and catalysis such as acidic properties (mainly Brønsted sites), redox and adsorption properties (due to the presence of oxygen vacancies) and a photostimulation response under visible light (2.6–2.8 eV bandgap). Depending on the operating condition of the catalytic process, each of these behaviors is tunable by controlling structure and morphology (e.g., nanoplates, nanosheets, nanorods, nanowires, nanomesh, microflowers, hollow nanospheres) and/or interactions with other compounds such as conductors (carbon), semiconductors or other oxides (e.g., TiO2) and precious metals. WOx particles can be also dispersed on high specific surface area supports. Based on these behaviors, WO3-based catalysts were developed for numerous environmental applications. This review is divided into five main parts: structure of tungsten-based catalysts, acidity of supported tungsten oxide catalysts, WO3 catalysts for DeNOx applications, total oxidation of volatile organic compounds in gas phase and gas sensors and pollutant remediation in liquid phase (photocatalysis).

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Section: Silica-supported Tungsten Oxidesmentioning

confidence: 99%

Section: General Overviewmentioning

confidence: 99%

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Tungsten-Based Catalysts for Environmental Applications

2021

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“…Among all the bands present on the spectra, the most important ones are those at 1 540 and ca. 1 450 cm À1 which are characteristic of Brønsted and Lewis acid sites respectively [54,55]. One can notice that the HSiW@SBA-15 catalyst contains only a very small amount of Brønsted acid sites compared to the three other solids which have quite the same amount of acid sites.…”

Section: Study Of the Acidity By Adsorption Of Pyridinementioning

confidence: 96%

Comparison of the Acidity of Heteropolyacids Encapsulated in or Impregnated on SBA-15

Pinto

Szeto

Oueslati

et al. 2016

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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-Heteropolyacids (HPA) immobilized onto SBA-15 silica were prepared by two different ways using either impregnation or encapsulation methodologies. Two Keggin-type HPA, H 3 PW 12 O 40 and H 4 SiW 12 O 40 were considered in this study. The resulting hybrid materials were fully characterized by N 2 adsorption-desorption isotherms, XRD, FT-IR, Raman, diffuse reflectance UV-Vis spectroscopies and 31 P MAS NMR. All characterization methods showed that at room temperature the catalysts contained well-dispersed and intact Keggin units throughout the solid. The catalytic activity of these solids was investigated in the isomerization of n-hexane. The impregnated and encapsulated phosphotungstic catalysts performed similarly in catalysis showing that the amount of active sites was nearly the same in both catalysts. On the contrary, the tungstosilicic encapsulated material was completely inactive while its impregnated counterpart was even more active than the phosphotungstic derived catalysts. The acidity of the solids was measured by various methods: microcalorimetry of ammonia adsorption, ammonia desorption followed by Temperature Programmed Desorption (TPD) and DRIFT/GC-MS and pyridine adsorption followed by infrared spectroscopy. Only pyridine adsorption and ammonia desorption followed by DRIFT/GC-MS agreed with the catalytic data. Ammonia adsorption followed by microcalorimetry was not able to differentiate between the four catalysts while the TPD experiments led to unreliable results, as not only the evolved ammonia but also other molecules such as water were taken into account in the measurements. The behavior difference between the encapsulated silico-and phosphotungstic acids was explained by a more pronounced encapsulation in the case of silicon. de préparation. L'activité catalytique de ces matériaux a ensuite été étudiée dans l'isomérisation du n-hexane.

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“…However, depending on the reaction temperature, the order of the catalytic activity was not same as the order of the acid amount, suggesting that the activity depends not only on the acid amount, but also on the acid type of the support materials and transition metal oxides. Zaki et al investigated the acidic properties of supported WO3 catalysts by pyridine adsorption and reported that strong Brønsted acid sites appeared on WO3/TiO2, whereas mainly Lewis acid sites existed on WO3/Al2O3 12) . Nb2O5/Al2O3 catalysts were reported to possess both Lewis acid sites and Brønsted acid sites 13) .…”

Section: Dme Hydrolysis Over Supported Solid Acidmentioning

confidence: 99%