Vanadium oxide supports

The reactivity of the supported vanadium oxide catalysts for other oxidation reactions also show similar trends as the oxide support is varied from titania to silica [13]. The activity and selectivity for partial oxidation products of vanadium oxide supported on titania being higher than vanadium oxide supported on silica. The oxidation activity of the supported vanadium oxide catalysts is related to the ability to donate oxygen to form the required oxidation products. The... 

To overcome the problems encountered in the homogeneous Wacker oxidation of higher alkenes several attempts have been undertaken to develop a gas-phase version of the process. The first heterogeneous catalysts were prepared by the deposition of palladium chloride and copper chloride on support materials, such as zeolite Y [2,3] or active carbon [4]. However, these catalysts all suffered from rapid deactivation. Other authors applied other redox components such as vanadium pentoxide [5,6] or p-benzoquinone [7]. The best results have been achieved with catalysts based on palladium salts deposited on a monolayer of vanadium oxide spread out over a high surface area support material, such as y-alumina [8]. Van der Heide showed that with catalysts consisting of H2PdCU deposited on a monolayer vanadium oxide supported on y-alumina, ethene as well as 1-butene and styrene... 

Raman Spectroscopy of Vanadium Oxide Supported on Alumina... 

The molecular state ot vanadium oxide supported on ditterent alumina phases (7, S-0, and a) was investigated with Raman spectroscopy. The supported vanadium oxide was "found to "form a molecularly dispersed overlayer on the di-f-ferent alumina phases. The molecular state oT the surTace vanadium oxide phase, however, was dependent on the nature oT the alumina support. This variation was primarily due to the presence oT surTace impurities, in particular sodium oxide. The surface sodium oxide content was found to increase with the calcination temperature required to form the different transitional alumina phases (a, 6-0, 7). The... 

FIGURE 5. Raman Spect-ra oF Vanadium Oxide Supported on 6,0-AI2O0. 

FIGURE 6. Raman Spectra oF Vanadium Oxide Supported on a-Al203. 

Khodakov, A., Olthof, B., BeU, A.T. and Iglesia, E. (1999) Structure and catalytic properties of supported vanadium oxides support effects on oxidative dehydrogenation reactions. Journal of Catalysis,... 

S. and Jackson, S.D. (2005) On the structure of vanadium oxide supported on aluminas UV and visible Raman spectroscopy, UV-visible diffuse reflectance spectroscopy, and temperature-programmed reduction studies. Journal of Physical Chemistry, 109, 2793-800. 

As shown in Fig. 8, the vibrational bands are clearly resolved in the photoluminescence spectrum of vanadium oxide supported on Vycor glass 33, 34, 36-38). The vibrational separation of about 1040 cm is in good agreement with the energy of the V=0 stretching vibration of the ground state of the vanadyl group of the oxide as measured by IR or Raman spectroscopies. 

Fk . 8. Vibrational fine structure of the photolumincscencc of vanadium oxide supported on porous Vycor glass at 77 K inset shows its vibrational progression [reproduced with permission from Kubokawa and Anpo (6i)]. 

As shown in Fig. 19, vanadium oxide supported on Vycor glass exhibits a photoluminescence spectrum at about 400-600 nm upon excitation of the absorption band at about 320 nm (33, 34, 63, 69,115,116). The absorption and photoluminescence spectra are represented by Eq. (12). The addition of 62, CO, N2O, C2H4, CsHg, or QHjj to the catalyst led to the quenching of the photoluminescence with differing efficiencies but without any changes in the shape of the spectrum. 

In this work, the activity and selectivity of catalysts based on niobium and vanadium oxides supported on high surface area anatase Ti02 in ethane ODH have been investigated. Specifically, the influence of the cooperation of vanadium and niobium oxides supported phases as components inducing respectively redox and acid properties, together with the effect of the preparation conditions on the catal3dic performances have been studied. 

The interaction between the two supported oxides can be modified by changing the preparation technique. By reversing the order of addition of vanadium and niobium at high V2O5 loading, catalysts having better performances can be obtained, while at low loading no effect has been found. This difference is hkely due to the different nature of vanadium oxide supported species. 

In particular, the study was centered on the analysis of the behavior in toluene selective oxidation of a series of V-containing micro- and mesoporous materials [mesoporous (MCM-41), MFI (2SM-5) and P type]. The formation of phenol as a by-product has also been observed in some cases. This product does not form in toluene oxidation over vanadium oxide supported on AI2O3 or TiOa [2-6] and is an interesting first example of the possibility of direct synthesis of phenol from toluene using gaseous O2. A further objective of this work therefore was to identify the key aspects in this reaction as well as the possible reaction mechanism. 

In this paper, we wish to report on the selective oxidation of 5-hydroxymethylfurfural to 2,5-furan-dicarboxaldehyde using vanadium oxide supported on titanium oxide with different vanadium loadings. If we take into account the large differences in the activation energies reported over V2O5 in the oxidation sequence benzyl alcohol --> benzaldehyde (Eg = 26 kJ/mol) and benzaldehyde > benzoic acid (Eg = 55 kJ/mol) [10], those catalytic systems were then expected to stop at the aldehyde stage by working at low temperatui e. 

Although the earlier workers undoubtedly felt that a somewhat milder form of catalyst than liad been used in the oxidation of naphthalene to produce phthalic anhydride would be necessary for the formation of anthraquinone, it was soon shown that vanadium catalysts were applicable. These catalysts consisting of vanadium oxides supported on pumice were used in tubular reaction chamber.28 Such disposition of the catalyst represented ail advance over the early method since it permitted a better control of gas rates and time of contact, a necessity when such active catalysts were used for the small degree of oxidation required in the reaction. A temperature range of 300° to 500° C. was specified and the use of diluent gases to control the reaction intimated. 

These results were compared to those obtained for vanadium oxide supported on Ga20s and MgO with comparable vanadium content. It was found that V-Mg-O-materials performed catalytically better and the V-Ga-O-materials performed worse than the V-Mg-Ga-O mixed metal oxides supported on AI2O3. Table 2 presents the catalytic performance of the best catalytic materials from V-Mg-Ga, V-Mg-0 and V-Ga-O solid material libraries. 

Centi G (1996) Nature of active layer in vanadium oxide supported on titanium oxide and control of its reactivity in the selective oxidation and ammoxidation of alkylaromatics. Appl Catal A 147 (2) 267-298... 

Deo, G., Wachs, 1. and Haber, J. (1994). Physical and Chemical Characterization of Surface Vanadium Oxide Supported on Titania Influence of the Titania Phase (Anatase, Rutile, Brookite), J. Crit. Rev. Surf. Chem., 4, pp. 27-42. 

Centi, G. (1996). Nature of Active Layer in Vanadium Oxide Supported on Titanium Oxide and Control of its Reactivity in the Selective Oxidation and Ammoxidation of Alkylaromatics, Appl. Catal. A Gen., 147, pp. 267-298. 

Lewandowska, A., Calatayud, M., Lozano Diz, E., et al. (2008). Comhining Theoretical Description with Experimental In Situ Studies on the Effect of Alkali Additives on the Structure and Reactivity of Vanadium Oxide Supported Catalysts, Catal. Today, 139, pp. 209-213. 

Khodakov, A., Olthof, B., Bell, A., etal. (1999). Structure and Catalytic Properties of Supported Vanadium Oxides Support Effects on Oxidative Dehydrogenation Reactions, J. Catal., 181, pp. 205-216. 

Initially, supported MoOx and VO species were proposed as active and relatively selective in the partial oxidation of methane to formaldehyde. The nature of metal oxide support and the V- or Mo-content strongly influence the dispersion of molybdenum and vanadium species, which is a key factor for obtaining better selectivity to formaldehyde. At the moment, the highest productivity to formaldehyde, in terms of space-time yields, seems to be obtained over a vanadium oxide supported on mesoporous silica synthesized by a novel method. In this case, the best results have been achieved with a water pressure of 8 kPa, suggesting that water mainly influences the number of accessible active sites and only weakly affects the catalytic properties of these sites. 

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