Ternary Phases with the Mo5O14 Type of Structure. I. A Study of the Molybdenum-Vanadium-Oxygen System.

Ekström, Thommy; Nygren, Mats; Simov, D.; Øye, H. A.; Svensson, Sigfrid

doi:10.3891/acta.chem.scand.26-1827

Cited by 50 publications

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“…Therefore we think that there are Mo 5 O 14 islands on the reduced catalyst surface. The lack of the distinct change in oxidation degree of molybdenum (5.60) during catalyst thermal treatment in oxygen reveals high resistance of Mo 5 O 14 to oxidation by O 2 , which agree well with earlier observations [18,30]. The use of the catalyst in the NO decomposition at 423 K in the oxygen presence causes a distinct increase of the contents and oxidation degrees of vanadium and molybdenum in the analysed nanolayers and some increase of the oxidation state of titanium.…”

Section: Resultssupporting

confidence: 90%

“…It should be noticed that ammonia forming as a result of the ammonium ions decomposition at the beginning of the precursor calcination acts as a reducer and can favour incorporation of the vanadium ions at lower degrees of oxidation into the anatase nanocrystallites or into the molybdenum oxide islands. Vanadium is known to dissolve well in the Mo 5 O 14 and MO 17 O 47 structures [18,19]. The unexpectedly intensive absorption at wavenumbers lowers than 16,000 cm_1 in UV-vis spectrum of the fresh catalyst also point to the presence of V ions at lower oxidation state in molybdenum oxide islands [28].…”

Section: Resultsmentioning

confidence: 99%

“…Thus, the formation of the mixed V + Mo/ anatase solid solution could also be expected. On the other hand, it is known that vanadia dissolves in some molybdenum sub oxides [18,19] whereas its dissolution in molybdena is rather low [20]. It was scheduled to obtain an anatase-supported V-O-Mo catalyst by preparing a solid solutions of molybdena and vanadia in anatase and possibly vanadia in some molybdenum oxide and next forming vanadia surface species via oxidation-induced surface V segregation.…”

Section: Introductionmentioning

confidence: 99%

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Surface species structure and activity in NO decomposition of an anatase-supported V–O–Mo catalyst

Kornelak¹,

Thomas²,

Camra³

et al. 2008

Catalysis Today

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The paper concerns the evolution of surface species of a V-O-Mo/anatase catalyst in the course of its thermal treatment in oxidising and/or reducing conditions. The catalyst was obtained by the sol-gel method. The structure of its surface was investigated by XPS and Raman spectroscopy. The fresh catalyst consists of anatase nanocrystallites with some vanadium and molybdenum ions substituted for titanium ones and molybdenum oxide islands on their surfaces. A V/Mo 5 O 14 solid solution-containing V atoms in its channels, as well as MoO 3 and anatase with some surface vanadia species are present on the catalyst surface. The reduction of anatase to TiO 2_x and of MoO 3 to Mo 5 O 14 , accompanied by inward vanadium diffusion occurs during the catalyst interaction with ammonia at 523 K. The oxidation of the TiO 2_x but not Mo 5 O 14 and V reappearance in the surface channels take place during the interaction of the reduced catalyst with molecular oxygen. However, the oxidation of Mo 5 O 14 to MoO 3 occurs under the influence of atomic oxygen, formed by NO decomposition at 423 K. It is accompanied by the surface vanadia species formation. The activity of V ions of these species in NO decomposition is lower than of the surface interstitial ones. IntroductionAnatase-supported vanadia-based catalysts are the best catalysts for the selective catalytic reduction of NO x (x = 1 or 2) by ammonia (NH 3 -SCR) to N 2 and H 2 O in oxygen presence [1][2][3][4][5][6]. Anatase is known as a structural support for V2O5 catalysts due to the good crystallographic phase matching [7]. Anatasesupported vanadia-tungsta catalysts are commonly used to remove NO from stationary sources of emission. Molybdena-vanadia catalysts, though less active than vanadia-tungsta ones, are frequently used to reduce NO in off-gases containing arsenic [8]. Their resistance to poisoning by arsenic is much higher than the resistance of V-O-W catalysts. Vanadia surface species are commonly considered as responsible for the NH 3 -SCR activity of all the vanadia-based catalysts [1][2][3][4][5][6]. Structures of the vanadia surface species of European industrial catalysts -V 2 O 5 /TiO 2 for selective toluene oxidation to maleic anhydride and V 2 O 5 -WO 3 /TiO 2 one for NH 3 -SCR of NO x -were widely discussed in special issues of Catalysis Today [9,10]. It has recently been found that surface species of V-O-W/rutile catalyst with a vanadia structure show relatively high activity in direct NO decomposition to dinitrogen and dioxygen in oxygen presence at 423-453 K [11-13]. Such species are formed as a result of an vanadium segregation on the surfaces of the nanocrystallites of rutile and tungsten oxides during the thermal treatment of the catalyst in oxygen [14]. We expected that analogous species could be formed on anatase-supported V-O-Mo catalyst surface and could be active in NO decomposition in oxygen presence.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Surface species structure and activity in NO decomposition of an anatase-supported V–O–Mo catalyst

Kornelak¹,

Thomas²,

Camra³

et al. 2008

Catalysis Today

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show abstract

“…This mechanism has even been shown to proceed in the case of the reduction of α-or β-VOPO 4 to (VO) 2 P 2 O 7 , catalysts of mild oxidation of 1-butene or n-butane to maleic anhydride [50,51]. The second mechanism is responsible for the formation of pentagonal columns by extensive edge-sharing between polyhedra [45], and is common to W, Te, etc., oxides as well as, e.g., uranium molybdates [52]. In the examined conditions [11], oxalic acid was leading to the formation of 350°C).…”

Section: Discussionmentioning

confidence: 99%

“…Therefore, we shall assume that, as confirmed by LRS, θ- One of the main questions to answer is the formation of solid solutions in the metastable θ-phase, which is known to be stabilized by several cations to a given extent [45]. The maximum solubility is, e.g., 11 at.% of V, 9 at.% of Nb and up to 30 at.% of W. In Nb-free catalysts, θ may be stabilized as (V 0.07 Mo 0.93 ) 5 [34].…”

Section: Discussionmentioning

confidence: 99%

Oxidation of ethane to ethylene and acetic acid by MoVNbO catalysts

et al. 2005

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Oxyfunctionalization of Alkanes

Schunk

2008

Handbook of Heterogeneous Catalysis

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The sections in this article are Introduction Analyzing the Challenge of Heterogeneously Catalyzed Alkane Oxidation Analysis on a Microscopic Basis of the Critical Steps of Paraffin Oxidation Utilizing Solid Catalysts Utilizing Solid Catalysts A Activation of Oxygen and Paraffin B Models for the Active Site C The Role of Co ‐Feeds in the Educt Stream D The Role of the Crystalline Nature and the Admixture of Different Crystalline Phases for the Catalyst E The Role of the Acid–Base Interaction of Reactant and Catalyst Analysis of the Technical Challenges of Paraffin Oxidation Utilizing Solid Catalysts Conversion of Butane to Maleic Anhydride: An Overview of a Mature Technology Manufacturing Technologies for MA from n ‐Butane The VPO ‐Catalyst: Structural Basis and Synthetic Pathways The VPO ‐Catalyst: Reaction Pathways and Potential Active Sites of the Catalyst Propane Oxidation to Acrylic Acid and Acrylonitrile: Getting Closer to a Technical Solution Rutile‐Based Structures for Selective Propane Oxidation Complex Bronze Structures Based on Molybdenum for Selective Propane Oxidation Ethane to Acetic Acid: The Search for a Viable Pathway Outlook Acknowledgments

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Ternary Phases with the Mo5O14 Type of Structure. I. A Study of the Molybdenum-Vanadium-Oxygen System.

Cited by 50 publications

References 0 publications

Surface species structure and activity in NO decomposition of an anatase-supported V–O–Mo catalyst

Surface species structure and activity in NO decomposition of an anatase-supported V–O–Mo catalyst

Oxidation of ethane to ethylene and acetic acid by MoVNbO catalysts

Oxyfunctionalization of Alkanes

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