Interaction of Vanadia with Alumina and Titania during ultra-high intensity grinding at room temperature as evidenced from 51V NMR spectra

doi:10.1016/S0166-9834(00)81715-7

Applied Catalysis

Volume 63, Issue 1, 1990, Pages 191-195

https://doi.org/10.1016/S0166-9834(00)81715-7 Get rights and content

Abstract

The interaction of V₂O₅ with Al₂O₃ (concentration range 2.5-25% V₂O₅) and TiO₂ (concentration range 3–12% V₂O₅) during ultra-high intensity grinding at room temperature was characterized by ⁵¹V NMR spectroscopy. The treatment resulted in disappearance of the signal of the bulk V₂O₅ and the formation of a new, thermally fairly stable species having a chemical shift in the range —500 to —700 ppm. The same species prevailed on supported vanadia catalysts prepared by grafting or conventional impregnation calcination procedures. Only partial formation of the same structure was indicated during prolonged calcination of the untreated mixtures.

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Selective catalytic reduction of NO with NH<inf>3</inf> over V<inf>2</inf>O<inf>5</inf> supported on TiO<inf>2</inf> and Al<inf>2</inf>O<inf>3</inf>: A comparative study
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Citation Excerpt :
It also suggested that V2O5 could interact with anatase TiO2. More studies [25,26] were revealing that the solid-state reaction between V2O5 and anatase TiO2 includes two steps: mixing of the two oxides and calcination resulting in chemical interaction of V2O5 with the TiO2 surface and V–O–Ti bond formation. It can also be seen from the Fig. 3 that all the peaks of Al2O3 sample was due to the γ-Al2O3 [27].
This study aimed at investigating the interaction of V₂O₅ species with TiO₂ and Al₂O₃ supports to understand the effect of supports on SCR reaction. Analysis by XRD, BET, UV–vis, and DFT theoretical calculations, XPS, EPR and in situ DRIFT showed that the two kinds of supports could interact with V₂O₅. The interaction of electron excitation and charge transfer of supports to V₂O₅ species was important to the formation of the reduced V₂O₅. These aspects increased the formation of superoxide ions that could improve the NO oxidation over V₂O₅/TiO₂. It was responsible for the higher SCR catalytic activity of V₂O₅/TiO₂ than V₂O₅/Al₂O₃.
Oxidative dehydrogenation of ethylbenzene over vanadia-alumina catalysts in the presence of nitrous oxide: Structure-activity relationship
2005, Journal of Catalysis
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Previous studies have demonstrated that supported vanadia systems exhibit high activity and selectivity for alkane oxydehydrogenation [15–19]. The molecular structure and reactivity of alumina-supported vanadia catalysts have been extensively investigated in recent years for the selective oxidation of hydrocarbons [20–40]. The vanadia species on the alumina surface range from highly dispersed monovanadates to dimeric tetrahedral, polymeric vanadia, and V2O5 crystallites depending on the vanadia content.
A series of vanadia-alumina catalysts with different vanadia contents were prepared by a wet impregnation method. The influence of the local structure of vanadia in these catalysts on the oxidative dehydrogenation of ethylbenzene with nitrous oxide was investigated. The use of N₂O as a co-feed remarkably enhanced the styrene yield compared with the use of N₂. Characterization of these vanadia catalysts by XRD, FTIR, UV–vis, TPR, XPS, and ⁵¹V NMR techniques suggests that the nature of the VO_x species depends on the vanadia loading; the predominant species are monomeric vanadia at lower loadings, two-dimensional polyvanadates at intermediate loadings, and bulk-like V₂O₅ and AlVO₄ at higher loadings. The rate of oxidative dehydrogenation (ODH) of ethylbenzene per vanadium atom increases with vanadia loading and reaches a maximum at 10 wt%, the loading at which the surface predominantly contains polyvanadate species. The observed variation in the selectivity of products with vanadium loading indicates that the monomeric V⁵⁺ species favors dehydrogenation, whereas bulk-like V₂O₅ preferentially participates in the dealkylation of ethylbenzene. The vanadium species remains at a higher oxidation state in the presence of N₂O, leading to a higher styrene yield, than in a N₂ atmosphere. The ODH turnover rates increased with decreasing energy of the absorption edge in the UV–vis spectrum, at low VO_x coverages of less than one monolayer on the Al₂O₃ surface.
Preparation, characterization, and activity of Al<inf>2</inf>O <inf>3</inf>-supported V<inf>2</inf>O<inf>5</inf> catalysts
2004, Journal of Catalysis
A series of activated alumina-supported vanadium oxide catalysts with various V₂O₅ loadings ranging from 5 to 25 wt% have been prepared by wet impregnation technique. A combination of various physicochemical techniques such as BET surface area, oxygen chemisorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), thermal gravimetric analysis (TGA), and Fourier transform infrared (FTIR) were used to characterize the chemical environment of vanadium on the alumina surface. Oxygen uptakes were measured at 370 °C with prereduction at the same temperature, which appears to yield better numerical values of dispersion and oxygen atom site densities. XRD and FTIR results suggest that vanadium oxide exists in a highly dispersed state below 15 wt% V₂O₅ loading and in the microcrystalline phase above this loading level. TPR profiles of V₂O₅/Al₂O₃ catalysts exhibit only a single peak at low temperature up to 15 wt% V₂O₅. It is suggested that the low-temperature reduction peak is due to the reduction of surface vanadia, which has been ascribed to the tetrahedral coordination geometry of the V ions. TPR of V₂O₅/Al₂O₃ at higher vanadia loadings exhibited three peaks at reduction temperatures, indicating that bulk-like vanadia species are present for these catalysts only at higher vanadia loadings, with V ions in an octahedral coordination. The TPR profiles of V₂O₅/Al₂O₃ catalysts indicate that at loadings lower than 15% vanadia forms isolated surface vanadia species, while two-dimensional structure and V₂O₅ crystallites become prevalent in highly loaded (>15% V₂O₅) systems. Liquid-phase oxidation of ethylbenzene to acetophenone has been employed as a chemical probe reaction to examine the catalytic activity. Ethylbenzene oxidation results reveal that 15%V₂O₅/Al₂O₃ is more active than higher vanadia loading catalysts.
Formation of active sites for selective toluene oxidation during catalyst synthesis via solid-state reaction of V<inf>2</inf>O<inf>5</inf> with TiO<inf>2</inf>
2000, Journal of Catalysis
Interaction of V₂O₅ with TiO₂ during the preparation of V/Ti-oxide catalysts via solid-state reaction has been studied by means of in situ FT-Raman spectroscopy, HRTEM and XPS. This interaction results in the formation of monomeric vanadia species with vanadium in tetrahedral coordination. The bridging oxygen in the V–O–Ti bond is suggested to be responsible for the catalytic activity during the partial oxidation of toluene. The formation of the monomeric vanadia species correlates with the improved catalyst performance, characterized by reaction rate and selectivity to benzaldehyde and benzoic acid. Mechanical activation by intensive grinding of V₂O₅/TiO₂ mixture via ball milling was necessary for the interaction of the oxides during the calcination. The monomeric species formation was observed at a temperature as low as 523 K. The dynamics of V₂O₅/TiO₂ interaction strongly depends on the presence of moisture during the calcination. In dry oxidative atmosphere, a part of the monomeric species is rapidly formed. Then, the process slows down and becomes diffusion-controlled. During the calcination in humid oxidative atmosphere, quick amorphization of bulk crystalline V₂O₅ was observed followed by slow formation of the monomeric vanadia species.
Characterization of silica- and alumina-supported vanadia catalysts using temperature programmed reduction
1994, Journal of Catalysis
The nature of the vanadia-support interaction for silica and alumina-supported V₂O₅ catalysts was investigated using temperature programmed reduction (TPR), temperature programmed oxidation, and solid-state ⁵¹V NMR. Solid-state ⁵¹V NMR for the V₂O₅/SiO₂ catalysts indicated the presence of microcrystalline bulk-like vanadia species even at low vanadia loadings. Temperature programmed reduction of V₂O₅/SiO₂ exhibited multiple peaks. It is suggested that the low temperature peak is due to reduction of surface vanadia. This appears to be the case also for bulk V₂O₅. ⁵¹V NMR indicated that bulk-like vanadia species are present for V₂O₅/Al₂O₃ catalysts only at high vanadia loadings. Vanadia was more highly dispersed on alumina than on silica as evidenced by NMR and TPR. The two lowest temperature TPR peaks appear to be related to the reduction of surface vanadia on V₂O₅/Al₂O₃. It was found that for V₂O₅/Al₂O₃ the average oxidation state of V after reduction to 900°C is consistent with the stoichiometry V⁺⁵ → V⁺⁴, whereas the V₂O₅/SiO₂ catalysts exhibited 70% reduction of the V₂O₅ to V₂O₃ as did bulk V₂O₅. The amount of surface vanadium as determined by TPR correlates reasonably to the amount of tetrahedral V found by NMR. It is concluded that TPR provides an excellent means by which vanadia dispersion can be estimated on supported vanadia catalysts.
Surface vanadia species in V<inf>2</inf>O<inf>5</inf>-TiO<inf>2</inf> systems prepared by mechanically mixing: A Fourier transform infrared spectroscopy study
1993, Vibrational Spectroscopy
Surface vanadium-containing species supported on titania (97% rutile) prepared by manually grinding both oxides and calcined between 773 and 973 K in the presence of water vapour have been studied by Fourier transform infrared spectroscopy. The application of band-shape analysis to the overlapping and weak bands using a computer programme has provided information about the surface vanadium species existing in these samples. Up to four different species have been identified in samples calcined above 923 K.

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Interaction of Vanadia with Alumina and Titania during ultra-high intensity grinding at room temperature as evidenced from 51V NMR spectra

Abstract

Surf. Sci.

J. Mol. Catal.

Catal. Today

Interaction of Vanadia with Alumina and Titania during ultra-high intensity grinding at room temperature as evidenced from ⁵¹V NMR spectra