Structure and acidity of vanadium oxide layered on titania (anatase and rutile)

Hatayama, Fumikazu; Ohno, Takashi; Maruoka, T.; Ono, Takehiko; Miyata, Hisashi

doi:10.1039/ft9918702629

Cited by 51 publications

(35 citation statements)

References 11 publications

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“…Deposition of 0.2 ML vanadia on titania results in a slight decrease of the intensity of this peak without any change in the shape and position of the peak maximum. In the presence of vanadia this peak should be related to titanium as well as to vanadium Lewis acid sites in accordance with FTIRS data [28,29]. However, the presence of more strongly adsorbed pyridine (723 K) is evident in the TPD profile of the undoped catalyst.…”

Section: Vanadia/titania Catalysts Doped With Ksupporting

confidence: 60%

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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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Section: Vanadia/titania Catalysts Doped With Ksupporting

confidence: 60%

“…It is known that pyridine interacts with TiO 2 surface forming only adsorbed species on Lewis acid sites and no species associated with Brønsted acid sites [28,29]. Hence, the observed pyridine TPD profile from TiO 2 with a maximum at 573 K should be related to the Ti 4+ Lewis acid sites.…”

Section: Vanadia/titania Catalysts Doped With Kmentioning

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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“…Surface acid-base properties are characterised via temperature-programmed desorption (TPD) of pyridine with mass spectrometric analysis of the products. This technique gives additional information as compared to the studies performed without gas-phase analysis [25][26][27][28]. The oxidation state and molecular structure of vanadia species are known to be influenced by the oxidative or reductive environment.…”

Section: Introductionmentioning

confidence: 98%

“…Chemisorption of pyridine is commonly used as a probe for the presence of Lewis and Brönsted acid sites on a catalyst surface [25][26][27][28]. Brönsted acid sites are associated with hydroxyl groups and interact with pyridine molecule forming pyridinium ion (PyH + ), while Lewis acid sites (metal cations) coordinatively bind pyridine (PyL).…”

Section: Catalyst Characterisationmentioning

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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“…IR can also probe the interaction of vanadium oxide with the surface hydroxyl groups of the oxide support since hydroxyl groups give rise to intense infrared [76][77][78][79][80][81][82][83][84][85][86]. Vanadium-oxygen vibrations are present below 1100 cm −1 and RS has the advantage that the support oxides only show weak absorption bands in the 700-1100 cm −1 region.…”

Section: Characterization Methods For Supported Vanadium Oxidesmentioning

confidence: 99%

Chemistry, Spectroscopy and the Role of Supported Vanadium Oxides in Heterogeneous Catalysis

Weckhuysen

Keller

2003

ChemInform

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Supported vanadium oxide catalysts are active in a wide range of applications. In this review, an overview is given of the current knowledge available about vanadium oxide-based catalysts. The review starts with the importance of vanadium in heterogeneous catalysis, a discussion of the molecular structure of vanadium in water and in the solid state and an overview of the spectroscopic techniques enabling to study the chemistry of supported vanadium oxides. In the second part, it will be shown that advanced spectroscopic tools can be used to obtain detailed information about the coordination environment and oxidation state of vanadium oxides during each stage of the life-span of a heterogeneous catalyst. Three topics will be discussed: (1) the molecular structure of supported vanadium oxide catalysts under hydrated, dehydrated and reduced conditions, including the parameters, which influence the molecular structures formed at the surface of the support oxide; (2) elucidation of the active surface vanadium oxide during the oxidation of methanol to formaldehyde, the reaction mechanism and the vanadium oxide-support effect; and (3) deactivation of fluid catalytic cracking (FCC) catalysts by migration of vanadium oxides and the development of a method preventing the structural breakdown of zeolites by trapping the mobile vanadium oxides in an aluminum oxide coating.

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Structure and acidity of vanadium oxide layered on titania (anatase and rutile)

Cited by 51 publications

References 11 publications

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

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

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

Chemistry, Spectroscopy and the Role of Supported Vanadium Oxides in Heterogeneous Catalysis

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