On the role of monomeric vanadyl species in toluene adsorption and oxidation on V2O5/TiO2 catalysts: a Raman and in situ DRIFTS study

Besselmann, S.; Löffler, Elke; Mühler, Martin

doi:10.1016/s1381-1169(00)00307-1

Cited by 169 publications

(76 citation statements)

References 41 publications

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“…3). It was shown by DRIFTS that toluene could be activated by the monomeric species while another type of vanadia species, containing oxygen for an insertion (polymeric and V 2 O 5 ) is necessary [36]. Thus, the monomeric species seems to possess the Lewis acidity suitable for toluene activation.…”

Section: Toluene Activationmentioning

confidence: 99%

Implication of the acid–base properties of V/Ti-oxide catalyst in toluene partial oxidation

Kiwi‐Minsker

Bulushev

Rainone

et al. 2002

Journal of Molecular Catalysis A: Chemical

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The work presents the effect of K-doping on V/Ti-oxides taking into account: the surface acid-base properties and the structure of surface vanadia species in respect to the catalyst performance and deactivation. The structure of active surface species determines redox properties, which are related to the catalytic performance by the Mars-van Krevelen mechanism. The reducibility of surface vanadia is studied by temperature-programmed reduction (TPR) in H 2 . The molecular structure of surface vanadia is determined by FT-Raman spectroscopy in a controlled atmosphere. Surface acid-base properties are characterised via temperature-programmed desorption (TPD) of pyridine with mass spectrometric analysis of the products.Transient response techniques with continuous monitoring of the composition of gaseous phase are applied to follow the catalyst surface transformations. Evolution of benzaldehyde (BA) formed during interaction of toluene with the pre-oxidised catalyst (without gaseous oxygen) gives information about the nucleophilicity of surface oxygen. Addition of potassium to surface vanadia leads to an increased oxygen nucleophilicity, resulting in a higher selectivity towards BA formation.In general, increase in surface basicity decreases catalytic activity, but at the same time the catalyst deactivation due to coking is suppressed. This allows catalyst optimisation in view of a better control of the partial oxidation process.

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Section: Toluene Activationmentioning

confidence: 99%

Implication of the acid–base properties of V/Ti-oxide catalyst in toluene partial oxidation

Kiwi‐Minsker

Bulushev

Rainone

et al. 2002

Journal of Molecular Catalysis A: Chemical

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“…It is known that treatment of V/Ti-oxides in aqueous solutions of bases and acids results in partial removal of vanadia from the catalyst surface (2,4,(14)(15)(16)(17). The dissolution of bulk V 2 O 5 and polymeric species has been reported extensively (2).…”

Section: Introductionmentioning

confidence: 99%

“…Spectroscopic information on the structure of insoluble species is quite limited (4). Recently Besselmann et al (17) found only the monomeric species with tetracoordinated vanadium on the Eurocat V/Ti-oxide catalysts after treatment by NH 4 OH by Raman spectroscopy under dehydrated conditions. However, octahedral vanadium coordination followed from the 51 V NMR studies of the HNO 3 -treated V/Ti-oxide catalyst (16).…”

Section: Introductionmentioning

confidence: 99%

Characterization of Surface Vanadia Forms on V/Ti–Oxide Catalyst via Temperature-Programmed Reduction in Hydrogen and Spectroscopic Methods

Bulushev

Kiwi‐Minsker

Rainone

et al. 2002

Journal of Catalysis

100

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Surface vanadia species formed on vanadia/titania catalysts consisting of 0.2-2.6 monolayers (ML) of VO x have been characterized by FT-Raman spectroscopy under controlled atmosphere, temperature-programmed reduction in hydrogen (TPR), and solubility in diluted HNO 3 . Three types of species were observed with the maximum peak temperatures as follows: isolated monomeric species (≤770-780 K), polymeric species (810 K), and bulk amorphous V 2 O 5 (852 K). During the reduction, the V= =O bond of the monomeric species with tetracoordinated vanadium disappears as shown by diffuse reflectance infrared Fourier transform spectroscopy. A formation of new hydroxyl groups with a basic character was observed. The monomeric species was found to be chemically stable with respect to diluted HNO 3 . Bulk amorphous V 2 O 5 and polymeric vanadia were soluble in HNO 3 and removed from the surface. The state of vanadium in the oxidized catalysts was mainly pentavalent, as shown by XPS, and did not change after acid treatment. Reduction by hydrogen of monolayer vanadia in a 0.2-ML V/TiO 2 catalyst was studied by temperature-programmed reduction (TPR) at different heating rates. A one-site kinetic model is able to account for the TPR data, in spite of the presence of the monomeric and polymeric species. This indicates that these species could be considered equal with respect to the interaction with hydrogen. The activation energy was determined for the catalyst reduction (98 ± 5 kJ/mol).

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“…The treatment of V/Ti-oxides in aqueous solutions of acids and bases results in partial removal of vanadia from the surface [2,4,[14][15][16][17]. The removal of bulk V 2 O 5 and polymeric species has been already reported [2,18].…”

Section: Introductionmentioning

confidence: 94%

“…Octahedral vanadium coordination www.elsevier.com/locate/cattod Catalysis Today 96 (2004) [195][196][197][198][199][200][201][202][203] followed from the 51 V NMR studies of the HNO 3 treated V/Tioxide [16]. However, isolated monomeric species with tetracoordinated vanadium was found by Raman spectroscopy in the Eurocat V/Ti-oxide catalysts after treatment in NH 4 OH [17]. The contradiction [16,17] could be assigned to the conditions of measurement (hydrated/dehydrated [1]) and to the different vanadia concentration in the samples remained after treatment.…”

Section: Introductionmentioning

confidence: 99%

Partial oxidation of toluene to benzaldehyde and benzoic acid over model vanadia/titania catalysts: role of vanadia species

2004

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Pure and K-doped vanadia/titania prepared by different methods have been studied in order to elucidate the role of vanadia species (monomeric, polymeric, bulk) in catalytic toluene partial oxidation. The ratio of different vanadia species was controlled by treating the catalysts in diluted HNO 3 , which removes bulk vanadia and polymeric vanadia species, but not the monomeric ones, as was shown by FTRaman spectroscopy and TPR in H 2 . Monolayer vanadia species (monomeric and polymeric) are responsible for the catalytic activity and selectivity to benzaldehyde and benzoic acid independently on the catalyst preparation method. Bulk V 2 O 5 and TiO 2 are considerably less active. Therefore, an increase of the vanadium concentration in the samples above the monolayer coverage results in a decrease of the specific rate in toluene oxidation due to the partial blockage of active monolayer species by bulk crystalline V 2 O 5 . Potassium diminishes the catalyst acidity resulting in a decrease of the total rate of toluene oxidation and suppression of deactivation. Deactivation due to coking is probably related to the Brønsted acid sites associated with the bridging oxygen in the polymeric species and bulk V 2 O 5 . Doping by K diminishes the amount of active monolayer vanadia leading to the formation of non-active K-doped monomeric vanadia species and KVO 3 . # 2004 Elsevier B.V. All rights reserved.

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On the role of monomeric vanadyl species in toluene adsorption and oxidation on V2O5/TiO2 catalysts: a Raman and in situ DRIFTS study

Cited by 169 publications

References 41 publications

Implication of the acid–base properties of V/Ti-oxide catalyst in toluene partial oxidation

Implication of the acid–base properties of V/Ti-oxide catalyst in toluene partial oxidation

Characterization of Surface Vanadia Forms on V/Ti–Oxide Catalyst via Temperature-Programmed Reduction in Hydrogen and Spectroscopic Methods

Partial oxidation of toluene to benzaldehyde and benzoic acid over model vanadia/titania catalysts: role of vanadia species

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