Structure and reaction studies on vanadium molybdenum mixed oxides

Adams, Andreas H.; Haaß, Frank; Buhrmester, Thorsten; Kunert, Jan; Ott, Jörg; Vogel, Herbert; Fueß, H.

doi:10.1016/j.molcata.2004.02.005

Cited by 26 publications

(14 citation statements)

References 10 publications

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“…Activity drops as soon as the lattice oxygen is consumed. 11,23,31 TP reductions confirm that catalysts with a molar ratio of Mo/V of 3 exhibit the best performance. 11,23 The integral evaluation of the AA production ( Fig.…”

Section: Reductive Conditionsmentioning

confidence: 80%

“…11,23,31 TP reductions confirm that catalysts with a molar ratio of Mo/V of 3 exhibit the best performance. 11,23 The integral evaluation of the AA production ( Fig. 6) shows the influence of the drying method and that W does not only serve as structural promoter but influences selectivity and activity significantly.…”

Section: Reductive Conditionsmentioning

confidence: 80%

“…After the calcination procedure the pellets were quenched in liquid nitrogen to stabilise the crystalline phases formed. The details of the solid state preparation can be found in Adams et al 22,23 Hydrochemical preparation routes. The second method of preparation is based on aqueous solutions of the ammonium salts acidified with nitric acid.…”

Section: Preparation Techniques For Mixed Oxide Catalystsmentioning

confidence: 99%

“…29 Orthorhombic MoO 3 is found in samples with high Mo contents 0.9 r x r 1 for the crystallised and at x = 1 for the spray-dried samples. 23 The spray-dried sample with Mo content x = 1 contains monoclinic V 6 O 13 , SG C2/m, 30 and orthorhombic V 2 O 5 types.…”

Section: Preparation Techniques For Mixed Oxide Catalystsmentioning

confidence: 99%

“…When conversion of ACR starts at 400 1C only total oxidation products are detected. 23,31 A typical concentration profile with a spray-dried model catalyst (V 2 Mo 8 W 3 O z ) is presented in Fig. 10.…”

Section: ''Reactive'' Conditionsmentioning

confidence: 99%

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Heterogeneously catalysed partial oxidation of acrolein to acrylic acid—structure, function and dynamics of the V–Mo–W mixed oxides

Kampe

Giebeler

Samuelis

et al. 2007

Phys. Chem. Chem. Phys.

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The major objective of this research project was to reach a microscopic understanding of the structure, function and dynamics of V-Mo-(W) mixed oxides for the partial oxidation of acrolein to acrylic acid. Different model catalysts (from binary and ternary vanadium molybdenum oxides up to quaternary oxides with additional tungsten) were prepared via a solid state preparation route and hydrochemical preparation of precursors by spray-drying or crystallisation with subsequent calcination. The phase composition was investigated ex situ by XRD and HR-TEM. Solid state prepared samples are characterised by crystalline phases associated to suitable phase diagrams. Samples prepared from crystallised and spray-dried precursors show crystalline phases which are not part of the phase diagram. Amorphous or nanocrystalline structures are only found in tungsten doped samples. The kinetics of the partial oxidation as well as the catalysts' structure have been studied in situ by XAS, XRD, temperature programmed reaction and reduction as well as by a transient isotopic tracing technique (SSITKA). The reduction and re-oxidation kinetics of the bulk phase have been evaluated by XAS. A direct influence not only of the catalysts' composition but also of the preparation route is shown. Altogether correlations are drawn between structure, oxygen dynamics and the catalytic performance in terms of activity, selectivity and long-term stability. A model for the solid state behaviour under reaction conditions has been developed. Furthermore, isotope exchange experiments provided a closer image of the mechanism of the selective acrolein oxidation. Based on the in situ characterisation in combination with micro kinetic modelling a detailed reaction model which describes the oxygen exchange and the processes at the catalyst more precisely is discussed.

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Section: Reductive Conditionsmentioning

confidence: 80%

Section: Reductive Conditionsmentioning

confidence: 80%

Section: Preparation Techniques For Mixed Oxide Catalystsmentioning

confidence: 99%

Section: Preparation Techniques For Mixed Oxide Catalystsmentioning

confidence: 99%

Section: ''Reactive'' Conditionsmentioning

confidence: 99%

See 3 more Smart Citations

Heterogeneously catalysed partial oxidation of acrolein to acrylic acid—structure, function and dynamics of the V–Mo–W mixed oxides

Kampe

Giebeler

Samuelis

et al. 2007

Phys. Chem. Chem. Phys.

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Interplay between Defect Structure and Catalytic Activity in the Mo_10−xV_xO_y Mixed‐Oxide System

et al. 2011

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The Mo(10-x)V(x)O(y) solid-solution systems (0≤x≤10) were studied by electron paramagnetic resonance spectroscopy. The results show the existence of paramagnetic vanadyl VO(2+) species, whose concentration becomes maximal for Mo(5)V(5)O(y·). A quantitative analysis of the [VO(2+)] concentration as a function of the Mo/V ratio allows it to characterize the prevailing defect chemistry in the Mo(10-x)V(x)O(y) system. In this respect, the semi-conducting properties of Mo(10-x)V(x)O(y) are p-type in an interval of Mo(9)V(1)O(y)-Mo(5)V(5)O(y) and switch into n-type because of the conduction electrons in a composition range of Mo(5)V(5)O(y)-Mo(1)V(9)O(y). Highest catalytic activity is obtained when vanadium acts as an acceptor center and oxygen vacancies ν(··)(O) are formed for reasons of charge compensation. In addition to the surface, ν(··)(O) and VO(2+) centers in the bulk have to be considered too for heterogeneous catalysis.

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Characterization of Mo‐V‐W Mixed Oxide Catalysts by ex situ and in situ X‐Ray Absorption Spectroscopy

Schimanke

Martin

Kunert

et al. 2005

Zeitschrift anorg allge chemie

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Mixed oxides in the system Mo‐V‐W‐O are important catalysts for partial oxidation reactions, e.g. the partial oxidation of acrolein to acrylic acid. Multiphase catalysts of the overall composition Mo8V2WyOx were prepared by spray drying and crystallization. The charge states of the potential catalytic centers Mo, V and W were investigated by ex situ X‐ray absorption spectroscopy (XAS). In the as prepared samples the cations exist essentially as Mo6+, V5+ and W6+. Exposure of the as prepared samples to acrolein results in a reduction of both Mo6+ and V5+ whereas W6+ is inert. Re‐oxidation with oxygen causes a reversible oxidation of Mo and V. The kinetics of the reduction and re‐oxidation processes of the catalyst samples was studied at a temperature of 500 °C by in situ X‐ray absorption spectroscopy at the Mo K‐edge with carbon monoxide and oxygen as reducing and oxidizing gases. The in situ experiments show that the reduction of Mo6+ in CO is about one order of magnitude slower than the subsequent re‐oxidation in oxygen.

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Structure and reaction studies on vanadium molybdenum mixed oxides

Cited by 26 publications

References 10 publications

Heterogeneously catalysed partial oxidation of acrolein to acrylic acid—structure, function and dynamics of the V–Mo–W mixed oxides

Heterogeneously catalysed partial oxidation of acrolein to acrylic acid—structure, function and dynamics of the V–Mo–W mixed oxides

Interplay between Defect Structure and Catalytic Activity in the Mo_10−xV_xO_y Mixed‐Oxide System

Characterization of Mo‐V‐W Mixed Oxide Catalysts by ex situ and in situ X‐Ray Absorption Spectroscopy

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Structure and reaction studies on vanadium molybdenum mixed oxides

Cited by 26 publications

References 10 publications

Heterogeneously catalysed partial oxidation of acrolein to acrylic acid—structure, function and dynamics of the V–Mo–W mixed oxides

Heterogeneously catalysed partial oxidation of acrolein to acrylic acid—structure, function and dynamics of the V–Mo–W mixed oxides

Interplay between Defect Structure and Catalytic Activity in the Mo10−xVxOy Mixed‐Oxide System

Characterization of Mo‐V‐W Mixed Oxide Catalysts by ex situ and in situ X‐Ray Absorption Spectroscopy

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Resources

About

Interplay between Defect Structure and Catalytic Activity in the Mo_10−xV_xO_y Mixed‐Oxide System