V2O5/AI2O3 catalyst

Figure 71.1 Raman spectra of supported V2O5/AI2O3 catalysts under dehydrated conditions as a function of vanadium oxide...

Figure 11.2 Concentration of polymeric surface VO, species for dehydrated supported V2O5/AI2O3 catalysts in the submonolayer region as a function of surface vanadium oxide density.

Figure 11.3 Number of exposed redox catalytic active sites for supported V2O5/AI2O3 catalysts as a function of vanadium oxide loading. Monolayer coverage corresponds to the 20% V2O5/AI2O3 (-7.9V atoms/nm ) catalyst sample.

Various reviews have discussed in detail the characterisbcs and performance of these catalysts and the reacbon mecharbsm in alkylaromabc ammoxidabon [93-95]. Over V2O5/AI2O3 catalysts, the reacbon mechanism proceeds via the... 

P5C-5 The kinetics of vapor-phase ammoxidation of 3-methylpyridine over a promoted V2O5-AI2O3 catalyst was reported in Chem. Eng. Sci., 35, 1425 (1980). Suggest a mechanism and rate-limiting step corrsisterrt with each of the two mechanisms proposed, hr each case how worrld yon plot the data to extract the rate law parameters Which mechanism is snpportedby the data ... 

However, the best yields of propylene are obtained on K-doped catalysts at high contact times (Fig. 7). This indicates that a lower rate in the combustion of propylene (consecutive reaction) is achieved on K-doped sample. In addition, since the maximum yield of propylene increases with the potassium content it can be concluded that on K-doped samples, the rate of consecutive reactions decreases in a longer extension than the formation of propylene, favoring the obtention of higher selectivites to ODH products (Fig. 6). Thus, the incorporation of potassium, remplacing Lewis acid sites on V2O5/AI2O3 catalysts, would eliminate nonselective sites in the deep oxidation of propylene. 

The effects of increasing space velocity have been demonstrated by Vassileva and co-workers [10]. The combustion of benzene over a 0.5 wt% Pd/30% V2O5/AI2O3 catalyst for space velocities of 330,2,000 and 5,000 h at a constant oxygen to benzene molar ratio of ca. 7.5. The effects of varying space velocity are shown in figure 2. However, it should be noted that these data indicate that there may be an induction period for this catalyst, which is most marked at the lowest space velocity investigated. 

V2O5/AI2O3 catalyst (DNllO, 10 wt% V2O5, Rhone-Poulenc) was used for a comparison. 

Qiao A, Kalevaru VN, Radnik J, Diivel A, Heitjans P, Hari Kumar AS, Sai Prasad PS (2014) Oxidative dehydrogenation of ethane to ethylene over V2O5/AI2O3 catalysts effect of source of alumina on the catalytic performance. Ind Eng Chem Res. doi 10.1021/ie5008344... 

Kiishnamoorthy, S. and Amiridis, M.D. Kinetic and in situ FTIR studies of the catalytic oxidation of 1,2-dichlorobenzene over V2O5/AI2O3 catalysts. Catal Today 1999, 51, 203-214. 

Gao L, Zhang D, Wang Y, Xue W, Zhao X (2011) Direct amination of toluene to toluidine with hydroxylamine over CUO-V2O5/AI2O3 catalysts. React Kinet Mech Catal 102 377-391... 

T.V.M. Rao and G. Deo, Kinetic parameter analysis for propane ODH V2O5/AI2O3 and M0O3/AI2O3 catalysts, AIChEJ., 53, 1538-1549 (2007). 

We have measured the differential heats of reoxidation and the reaction characteristics of a number of V2O5/Y-AI2O3 catalysts. The chemical transformation corresponding to the heat measurement in this system is ... 

For various types of catalyst there are results of kinetic investigations for the oxidative dehydrogenation of ethane available (e.g., for a magnesium oxide catalyst doped with samarium oxide, lithium nitrate and ammonium chloride [64] or a V2O5/Y-AI2O3 catalyst [68]). In another study with a Sn.oLai.oNdi.oOx catalyst, investigations were reported of noncatalytic reactions, which were found to be significant at temperatures above 700 °C [69]. 

The acid-base properties of V2O5/7-AI2O3 catalysts prepared by the impregnation method have been characterized by ammonia, pyridine and sulfur dioxide adsorption microcalorimetry. Sulfur dioxide adsorption made it possible to differentiate a vanadate layer from free alumina. 

A 20wt% V2O5/Y-AI2O3 catalyst has been subjected to a TPR in ethane and reoxidation in air using TG-DSC equipment, and compared to bulk vanadium pent-oxide. Reduction in ethane occurs at a lower temperature on the V2O5/Y-AI2O3 catalyst (717 compared with 794 K for bulk vanadium pentoxide). The exothermic... 

The role of metal oxides as promoters of V2O5/Y-AI2O3 catalysts in the oxidative dehydrogenation of propane... 

The physicochemical properties of potassium-, bismuth-, phosphorous- and molybdenum-doped (MeA7 atomic ratios of 0 to 1) V2O5/Y-AI2O3 catalysts and their catalytic behavior in the oxidative dehydrogenation of propane have been compared. The incorporation of metal oxides modifies the catalytic behavior of alumina-supported vanadia catalysts by changing both their redox and their acid-base properties. In this way, the addition of potassium leads to the best increase in the selectivity to propylene. This performance can be related to the modification of the acid character of the surface of the catalysts. The possible role of both redox and acid-base properties of catalysts on the selectivity to propylene during the oxidation of propane is also discussed. 

Figure 4. Variation of the selectivities to propylene ( ) CO ( ) and CO2 ( ) in the ODH of propane on a V2O5/Y-AI2O3 catalyst (3.5 wt% V-atoms) at 500-500 C. Experimental conditions in text.

Supported vanadium oxide catalysts have some activity for the olefin metathesis reaction but are not very selective (Banks 1969). In combination with Rc207 a very active catalyst system is obtained with alumina as the support (Nakamura, R. 1977b Xu, X. 1985b). When V2O5/AI2O3 is preheated at about 575°C and treated with Me4Sn it forms an effective catalyst system (V/Al = 3/97 Sn/V = 0.05-0.08) for propene metathesis at 25°C (Ahn, H-G. 1993). 

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