Valence states of vanadia-on-titania/silica and molybdena-on-silica catalysts after reduction and oxidation

Biermann, J.J.P.; Janssen, F.J.J.G.; Ross, J.R.H.

doi:10.1021/j100386a021

Cited by 12 publications

(3 citation statements)

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“…X-ray photoelectron spectroscopy (XPS) provides information about the oxidation state and the chemical environment of a given atom due to shifts in the binding energies [97][98][99][100][101][102][103][104][105]. The structural information is, however, limited since XPS cannot discriminate between different VO x structures possessing the same oxidation state, i.e.…”

Section: Bm Weckhuysen De Keller / Catalysis Today 78 (2003) 25-46mentioning

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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Section: Bm Weckhuysen De Keller / Catalysis Today 78 (2003) 25-46mentioning

confidence: 99%

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

Weckhuysen

Keller

2003

ChemInform

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“…Several works presented results of investigations on the isothermal hydrogen reduction of V 2 O 5 /TiO 2 [23][24][25] and V 2 O 5 /TiO 2 + KHSO 4 [24]. In some cases, other reducing agents, such as CO [25], NH 3 [26][27][28], * Corresponding author.…”

Section: Introductionmentioning

confidence: 99%

Interaction of oxygen with the surface of vanadia catalysts

Słoczyński

Grabowski

Kozłowska

et al. 2007

Journal of Molecular Catalysis A: Chemical

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“…These include IR,6 XPS,10"12 ESR,6,10,11 and differential scanning calorimetry (DSC). 12 Most of these studies have been done with the catalysts at (or at least treated with the reagents at) temperatures greater than 573 K. Ammonia is the dominant reductant at these elevated temperatures according to the reaction (excluding gas-phase oxygen) 3V205 + 2NH3 -3V204 + N2 + 3H20…”

Section: Introductionmentioning

confidence: 99%

Partial reduction of a vanadia/silica-titania catalyst with ammonia + nitric oxide at 473 K studied by electrical conductance and ESR measurements

Björklund¹,

Andersson²,

Odenbrand³

et al. 1992

J. Phys. Chem.

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Partial reduction of vanadia supported on silica-titania by NH3 + NO has been studied by electrical conductance and ESR measurements. The relationship between electrical conductance and degree of reduction was determined by oxidative and reductive titrations of V(IV) and V(V) species leached from catalyst samples which had been reduced to different levels.In situ monitoring of the steady-state V(1V) ion concentration by electrical conductance during reduction with NH3 + NO in the concentration range M O O ppm for each reactant in a 2 vol 7% 02/Ar carrier gas was performed. In a large excess of NH,, the V(IV) ion concentration increased sharply with even small additions of NO. In a large excess of NO, the NH, + NO mixture exhibited first an oxidizing character, and the V(IV) ion concentration increased when PNHl > The reaction order with respect to the NO concentration, determined from both the NO conversion and the initial rate of catalyst reduction in excess NH3, was found to be less than unity. Determination of the stoichiometry of the reaction with respect to O2 indicated that the gas-phase O2 concentration required to balance the reducing character of NH3 + NO mixtures on the surface was significantly higher than predicted by the balanced equation describing the reaction. ESR measurements on the catalyst detected V(IV) ions as vanadyl groups having two different coordination spheres. Reduction of the catalyst with NH, + NO caused an increase in the V(IV) signal and a decrease of the hyperfine structure. latroduction Selective catalytic reduction of nitrogen oxides by ammonia (SCR) is an established technology for reducing emissions from sb,tatiow power stations, A thoroUa description of the catalysts and details of the reaction have recently been published.' Vanadia-based catalysts, supported on Ti02, exhibit high activity for the SCR reaction in the Presence of 1-6 VOl % oxygen. Commercial catalysts are promoted with tungstate to reduce the activity for oxidation of SO,? and work has recently been reported on optimizing the catalyst pore structure to increase the resistance against SO2 and As203 p~isoning.~ Commercial reactors operate in the temperature range 620-670 K with water vapor concentrations of 6-12 vol %.

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Valence states of vanadia-on-titania/silica and molybdena-on-silica catalysts after reduction and oxidation

Cited by 12 publications

References 0 publications

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

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

Interaction of oxygen with the surface of vanadia catalysts

Partial reduction of a vanadia/silica-titania catalyst with ammonia + nitric oxide at 473 K studied by electrical conductance and ESR measurements

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