Vanadium oxide-based catalysts

Analysis of structure-activity relationships shows that various species characterized by different reactivities exist on the surface of vanadium oxide-based catalysts.339 The redox cycle between V5+ and V4+ is generally accepted to play a key role in the reaction mechanism, although opposite relationships between activity and selectivity, and reducibility were established. More recent studies with zirconia-supported vanadium oxide catalysts showed that vanadium is present in the form of isolated vanadyl species or oligomeric vanadates depending on the loading.345,346 The maximum catalytic activity was observed for catalysts with vanadia content of 3-5 mol% for which highly dispersed polyvanadate species are dominant. 

Catalytic properties of vanadium oxide based catalysts depend strongly on their ability to provide surface oxygen as a reactant. Therefore, theoretical studies of physical and chemical (catalytic) properties of the structurally different surface oxygen centers can help to elucidate details of the reaction steps. Moreover, calculations of electronic, structural, and energetic properties of oxygen vacancies created by oxidation reactions are of vital importance as will be discussed in the following. 

Supported metal oxides are currently being used in a large number of industrial applications. The oxidation of alkanes is a very interesting field, however, only until recently very little attention has been paid to the oxidation of ethane, the second most abundant paraffin (1). The production of ethylene or acetaldehyde from this feed stock is a challenging option. Vanadium oxide is an important element in the formulation of catalysts for selective cataljdic reactions (e. g. oxidation of o-xylene, 1-3, butadiene, methanol, CO, ammoxidation of hydrocarbons, selective catalytic reduction of NO and the partial oxidation of methane) (2-4). Many of the reactions involving vanadium oxide focus on the selective oxidation of hydrocarbons, and some studies have also examined the oxidation of ethane over vanadium oxide based catalysts (5-7) or reviewed the activity of vanadium oxide for the oxidation of lower alkanes (1). Our work focuses on determining the relevance of the specific oxide support and of the surface vanadia coverage on the nature and activity of the supported vanadia species for the oxidation of ethane. 

The catalyst chemistry of alkyl aromatic ammoxidation has been extended to other alkyl substrates in addition to toluene and lenes. The effectiveness of vanadium oxide-based catalysts to selectively catalyze the conversion of methyl groups attached to aromatic rings is wide-ranging. An example is the ammoxidation of alkyl naphthalenes, notably the ammoxidation of 2,6-dimethylnaphthalene to the corresponding dicyanonaphthalene. 

Flame synthesis of nanostructured vanadium oxide based catalysts... 

The monomers discussed in this section are derived from maleic acid (MA, c -butenedioic acid) or fumaric acid (FA, tra 5-butenedioic acid). Whereas FA is present in the metabolism of mmierous plants, MA is not, but MA, in the form of its anhydride (MAH), is technically produced in large quantities in contrast to FA. The technical production of MAH (mp 52 to 53 °Q is based on the oxidation of benzene or butane with air in the presence of vanadium oxide-based catalysts. FA (mp 287 °Q is thermodynamically more stable than MA (mp 138 to 139 °C) by 22.8kJ/mol [915]. Therefore, FA is easily produced by catalytic isomerization of MA. 

Clerici, M.G. and Kholdeeva, O.A. (eds) (2013) Liquid Phase Oxidation via Heterogeneous Catalysis Organic Synthesis and Industrial Applications, John Wiley Sons, Inc., Hoboken. Bruckner, A. and Baems, M. (1997) Selective gas-phase oxidation of polycyclic aromatic hydrocarbons on vanadium oxide-based catalysts. Appt Catal. A- Gen., 157 (1-2), 311-334. Corma, A., Esteve, P., and Martinez, A. (1996) Solvent effects during the oxidation of olefins and alcohols with hydrogen peroxide on Ti-beta catalyst the influence of the hydrophilicity-hydrophobicity of the zeolite. /. Catal, 161 (1), 11-19. 

Ballarini, N., Cavani, R, Cericola, A., et al. (2004). Supported Vanadium Oxide-based Catalysts for the Oxidehydrogenation of Propane under Cyclic Conditions, Catal. Today, 91-92, pp. 99-104. 

Mamedov, E. and Cortes Corberan, V. (1995). Oxidative Dehydrogenation of Lower Alkanes on Vanadium Oxide-based Catalysts. The Present State of the Art and Outlooks, Appl. Catal. A Gen., 127, pp. 1 10. 

Lemonidou, A., Nalbandian, L. andVasalos, 1. (2000). Oxidative Dehydrogenation of Propane over Vanadium Oxide Based Catalysts Effect of Support and Alkali Promoter, Catal. Today, 61, pp. 333-341. 

Moreover, the application of oxygen chemisorption techniques assumes that reduced surface transition metal species are responsible for the catalytic activity [4], However, detailed investigation through successive cycles of reactant adsorption and temperature programmed surface reaction (TPSR) without reoxidation of the surface showed the deactivation of molybdenum and vanadium oxide-based catalysts upon reduction [9]. These results clearly indicate that oxidized surface metal oxide species are the active surface sites to be investigated. 

This observation led Murakami and coworkers to develop a new method to measure the concentration of V=0 species on oxidized vanadium oxide-based catalysts [10,11]. The method known as rectangular pulse technique involves the reaction of NO and NH3 with surface V=0 species to produce molecular nitrogen according to the following stoichiometric reaction ... 

Mamedov, E.A. and Cortes Corberan, V. Oxidative dehydrogenation of lower alkanes on vanadium oxide-based catalysts. The present state of the art and outlooks. Catal. A Gen. 1995, 127, 1. 

The role of M0O3 as a promoter has been explained as a moderator for benzene oxidation. Bhattacharya and Venkataraman studied a variety of vanadium oxide-based catalysts. They concluded that, under their conditions, the best yields of MA were obtained using the composition V2O5 (1-2.3) Mo03 (1.0), supported on kieselguhr, with 5% cobalt oxide as a promoter. 

Multicomponent (P04)jf(V205), catalysts are applied in processes to produce maleic anhydride and phthalic anhydride intermediates for polymers. In the classical industrial process, maleic anhydride is the product from benzene and phthalic anhydride the product from naphthalene. Vanadium oxide-based catalysts have a stronger interaction with their substrates than molybdenum oxide-based catalysts. Whereas on M0O3 catalysts the hydrocarbon skeleton remains intact, oxidation on vanadium oxides proceeds with rupture of carbon-carbon bonds and the total number of carbon atoms in the molecule is not maintained in the reaction products. A new development is the use of butane as a reactant in these processes. 

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