Rutile-Type Catalyst

There are three Ti02 polymorphs, namely, rutile, anatase, and brookite an additional synthetic phase called Ti02 (B) and some high-pressure polymorphs have been also reported [45,46], Both the rutile and anatase polymorphs have photocatalytic properties however, these properties are more developed in the anatase polymorph [46], 

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The catalyst composition has a role in the control of selectivity. The rutile-type V/Sb/(Nb) mixed oxide activates the hydrocarbon and ammonia. However, most of the ammonia is burnt to N2, rather than being inserted on the hydrocarbons this likely occurs because the catalyst is not veiy efficient in the generation of the selective Me=NH species when reaction temperatures lower than 400°C are used (11). In fact, with all catalysts the selectivity to A -containing compounds increased when the reaction temperature was increased, and the selectivity to N2 correspondingly decreased (Figure 40.6). The dilution of the active phase with tin... 

Rutile-type Cr antimonate, CrSb04, is fairly active and selective in propane ammoxidation in catalysts studied by Snamprogetti, adding V considerably improves... 

Tin (IV) oxide, Sn02, (rutile-type structure), a well-established n-type semiconductor with a wide band gap ( gap = 3.6 eV at 300 K) also has potential applications as a catalyst support,as transparent conducting electrodes,and as a gas sensor.i This material possesses many advantages, such as (i) high thermodynamic stability in air (at least up to 500 °C), (ii) low cost, and (iii) the possibility of the introduction of catalysts or dopants to enhance the sensitivity or selectivity. ... 

FT-IR spectra of the four samples are reported in Figure 1. The catalysts prepared by coprecipitation (1,2,3) have the same FTIR spectra. It is possible to see the stretching absorbance of the V=0 bond at around 988 cm this shifting to lower frequencies with respect to the absorbance of the crystalline V2O5 (1022 cm l) may be attributed to two effects, firstly to the interactions between the vanadyl species and the rutile type Sn02 matrix and... 

Values of catalyst concentration for 0.2% transmittance are included in the last column of Table 4.4. It can be noticed that the effective specific extinction coefficients range from 2.6 10 cm g for the Rutile 1 catalyst to 1.32 lO cm g for Degussa P25, with the photocatalysts with higher extinction coefficients requiring lower catalyst concentrations to reach the condition of 0.2% of qac o.z.tk-, Thus, it can be infeired that the type of catalyst used significantly affects the concentration needed to achieve the condition 0.2% of qac h,z. t c, ... 

Andersson, A., Hanse, S. and Wickman, A. (2001). The Importance of Site Isolation and Phase Cooperation in Propane Ammoxidation on Rutile-type Vanadia Catalysts, Top. Catal., 15, pp. 103-110. 

One important characteristic of V-Sb-0 based catalysts, initially developed for the partial ammoxidation of propane to acrylonitrile in the 1980s by BP, is the presence of cation-deficient rutile-type VSb04 (Fig. 24.2b) and a-Sb204 structures. Antimony is mainly present in a pentavalent state favoring a large amount of partially reduced vanadium species, with the formation of V Sb04 and the possible presence of in substitutional or interstitial solid solution coordinations. The... 

Typical propane ammoxidation catalysts are essentially constituted by a combination of metallic mixed oxides. To date, there are two catalytic systems i) vanadium-antimonates with a rutile-type structure, represented by the VSbxMyOz formula, where M are elements used as the promoter such as W, Al, Te, Nb, Sn, Bi, Cu, or andii) vanadium-molybdates with a bronze structure, rep-... 

Mimura, Y., Ohyachi, K., Matsuura, I., et al. ( 999).Selective Ammoxidation of Propane over Sb-Nb-V Oxide Catalysts with a-Si>2 O4 and Rutile Type Structure, Stud. Surf. Sci. Catal., 121, pp. 69-74. 

Table 9.2 summarizes the performance of some V/Sb/O-based catalysts [40b]. BP claimed the same catalyst type for propane-lean conditions, with high conversion of the paraffin, and propane-rich conditions. In these catalysts, the main component is the rjuasi-VSb04 rutile, which transforms the alkane into the unsaturated intermediate. The latter may either desorb to yield propene or be transformed into acrylonitrile over the SbOx overlayers, the amount of which is a function of the Sb in excess with respect to the rutile formula [24c]. 

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