Titania vanadium oxide

Ti02 nanotubes were used to support M0O3 observing a spontaneous dispersion of molybdenum-oxide on the surface of nanotubes, which was different from that observed on titania particles.Supporting tungsten oxides a preferential orientation of the (002) planes was observed. Vanadium-oxide in the form of nanorods could be prepared using the titania nanotube as structure-directing template under hydrothermal... 

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... 

The reactivity ot the titania supported vanadium oxide catalysts was probed by the methanol oxidation reaction. The oxidation ot methanol over the titania supported vanadia catalysts exclusively yielded tormaldehyde, 95%+, as the reaction product. The titania support in the absence ot surtace vanadia yielded dimethyl ether and trace amounts ot CO2 The almost... 

Other classes of catalysts investigated include supported Keggin-type P/Mo/V/O polyoxometalates [14-16], and titania-supported vanadium oxide or V/P/(Mo)/0... 

The decrease in activity of heterogeneous Wacker catalysts in the oxidation of 1-butene is caused by two processes. The catalyst, based on PdS04 deposited on a vanadium oxide redox layer on a high surface area support material, is reduced under reaction conditions, which leads to an initial drop in activity. When the steady-state activity is reached a further deactivation is observed which is caused by sintering of the vanadium oxide layer. This sintering is very pronounced for 7-alumina-supported catalysts. In titania (anatase)-supported catalysts deactivation is less due to the fact that the vanadium oxide layer is stabilized by the titania support. After the initial decrease, the activity remains stable for more than 700 h. 

The results of the above characterization studies indicate that also in titania-supported catalysts the vanadium oxide layer slightly sinters. Since the vanadium oxide dispersion strongly effects the activity of the catalyst [16], it is likely that this sintering process is causing the deactivation observed in Fig. 3. The TPR and TPD results show that also some carbonaceous deposits are formed under reaction conditions, but these deposits are only present in low concentrations and, therefore, not likely to cause the deactivation of the catalyst. 

Supported vanadium catalysts, whereby vanadium oxide is dispersed on a support such as alumina or titania are of particular importance in, for instance, the oxidative dehydrogenation of alkanes [58-64]. Such materials have attracted considerable interest in the direct dehydrogenation of butane, where a key driver is to identify the relationship between catalytic activity and structural properties [5, 6, 65-68]. In the pure (solid) metal oxides the coordination of vanadium is well defined. However, this is not necessarily true in the case of supported catalysts. Vanadium may be present on the support surface as isolated vanadium ions dimeric or polymeric species one- and two-dimensional chains of vanadium ions ... 

Apparently at a temperature above 300 C, the oxidation kinetics of NOx and ammonia gas is so fast that slip of the reactants, when fed from the opposite sides of an alumina or alumina-titania membrane, can be avoided. Vanadium oxide, used as the catalyst for the reaction, is impregnated onto the membrane pore surface. The conversion of NOx reach 70% with the selectivity for nitrogen up to 75% in the temperature range of 300 to 350 C [Zaspalis etal., I991d]. 

Performance improvement in 1102 is achieved by doping the titania with platinum or vanadium oxide and copper. In order to improve the adsorption characteristics of Ti02, attempts have been made to support fine Ti02 on the porous adsorbent materials such as silica, alumina, activated carbon, clay, and zeolites. Ti02-supported adsorbent provides higher specific surface area and introduces more effective adsorption sites than bare Ti02. Decomposition rates of the substrates are found to increase due to one or... 

Ciambelli et al. [75] proposed a model for the vanadium oxide monolayer on titania. At loadings of vanadia below 6 wt.-%, a species prevails. At higher loadings the number of species increases, and thus the number of Bronsted sites grows. 

The preparation and characterization of titania-supported vanadia catalysts have been reviewed by Bond and Flamerz Tahir and provide a guide to the literature on preparation, structure and catalytic properties of vanadium oxide monolayer catalysts [5]. Preparative methods such as grafting, heating mechanical mixtures, or coprecipitation are also discussed. 

The surface vanadium oxide species on silica, water-treated silica, alumina, ceria, titania, zirconia, niobia and titania-silica have been characterized and studied for the selective oxidation of ethane. 

Binary vanadium-titanium oxide catalysts with various ratios of vanadium oxide and titania, as well as individual oxides of vanadium and titanium were examined in oxidation of P-picoline. Nicotinic acid, 3-pyridinecarbaldehyde, and CO2 were the reaction products over all the catalysts. The binary catalysts and individual vanadium oxide were highly selective for nicotinic acid, the most effective in P-picoline oxidation were the samples containing 20% and more of vanadium pentoxide. A regular stacking of crystallites of V2O5 and Ti02 was found to be the characteristic feature of the structure of the most effective compositions. 

IR spectrum of individual titania and the IR spectra of the binary catalysts coincide well with the spectrum of anatase [8] at 200-1300 cm". However in the spectra recorded for individual Ti02 and the sample containing 5% of vanadium oxide, the maxima of broad absorption bands (a.b.) at 540 and 342 cm", which are characteristic of anatase, are shifted downfield to 517 and 332 cm , at the same time a.b. at 965 and 1050 cm with 1070 and 1125 cm shoulders, respectively, are observed, that indicates the presence of sulfate-ion... 

Fig.4 shows the selectivities for the reaction products and the rate of oxidation of P-picoline against composition of the vanadium-titania system. All the binary vanadium-titania catalysts and the individual vanadium oxide reveal high selectivities for nicotinic acid. The selectivity for nicotinic acid increases from 75 to 90% and the rate of p-picoline oxidation increases by three times as the concentration of V2O5 increases from 5 to 20%, no further... 

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