Vanadium-containing catalysts preparation

Figure 4. X-Ray diffraction patterns for phosphorous-vanadium oxide catalysts prepared by aerosol technique at 600 C, 8 seconds residence time, and 0.8 M V in feed a. Catalyst analyzed by XRD immediately after synthesis, b. catalyst calcined at 450°C in nitrogen for 3 hrs immediately after synthesis, c. Catalyst allowed to stand for 14 days in an air tight container at ambient temperature without calcining.

Organometallic usage is shown in the preparation of titanium- or vanadium-containing catalysts for the polymerization of styrene or butadiene by the reaction of dimethyl sulfate with the metal chloride (145). Free-radical activity is proposed for the quaternary product from dimethylaniline and dimethyl sulfate and for the product from l,l,4,4-tetramethyl-2-tetrazene and dimethyl sulfate (146,147). 

A series of vanadium phosphate catalysts prepared by various routes and containing various phases were examined by Guliants et al. (105). From this investigation, it was concluded that the catalytically active phase is an active surface layer on vanadyl pyrophosphate. The experimental results showed VOPO4 phases to be detrimental to the performance of the catalyst. 

The results obtained with vanadium oxide catalysts prepared by the impregnation method show a remarkable contrast with those obtained with anchored vanadium oxide catalysts (63,116). As shown in Fig. 64. the yields of the photocatalytic isomerization as well as the yields of the phosphorescence of the oxide increase with the content of the vanadium ions and then decrease, even when the catalyst contains 0.1 wt% V. When the vanadium content is high, an increase in the efficiency of the radiationless deactivation due to the aggregation of the vanadium oxide species is observed. 

Occelli, M. L. and Stencel, J. M., "Cracking Metals-Contaminated Oils with Catalysts Containing Metal Scavengers. Part II. The Effect of Aluminuma Particles Addition on Vanadium Passivation." (In preparation)... 

When discussing the suitability of the ARCO pilot unit for cracking atmospheric residues, this cannot be done without touching on the question about how to prepare the catalysts for testing. An equilibrium catalyst used in a commercial residue FCCU contains significant amounts of metal contaminants, especially nickel and vanadium. Fresh catalysts must therefore be impregnated with these metals and deactivated before the catalysts can be nsed in the pilot unit. We have shown that this... 

The syndiotactic polypropylenes prepared with soluble vanadium-based catalysts usually contain some irregular linkages of propylene units arranged in head-to-head (Eq. 31) and tail-to-tail (Eq. 32) sequences. Doi95) has shown that the syndiotactic triad fraction [rr] of polypropylene decreases with an increase of the amount of the irregular linkages of propylene units [F01 + F10] (see Figure 16). 

Samples of used residue hydrodemetallization catalysts prepared by hydrotreating a Safanyia atmospheric residue have been characterized and tested using model compounds in order to investigate the initial deactivation of the catalyst Samples containing 4 to 10 wt % carbon and less than 200 wt ppm V or 10 to 15 wt % carbon and 1.3 wt % V have been obtained from tests in batch and continuous flow reactors respectively. It is shown that in the early stage of the catalyst deactivation a small amount of vanadium is more deactivating than a large amount of carbon. 

In the reported experiments, transition metal ion concentrations were typically low, and electrolytes were added, and, hence, the results are not necessarily pertinent to industrial catalyst preparation. However, Raman spectroscopy was also applied for the characterization of mixed metal ion solutions with compositions of industrial relevance (Dieterle, 2001). Figure 7A, for example, shows the Raman spectra of solutions containing molybdenum, tungsten, and vanadium ions as a function of pH. At high pH values, for example, between 9 and 6, Raman bands were observed that evidence M0O42 and V10O286- species. Raman bands of hepta- and octa-molybdate, and decavanadate were observed upon acidification. At the pH... 

The chapters in Characterization and Catalyst Development An Interactive Approach, assembled from both academic and industrial contributors, give a unique perspective on catalyst development Some chapters thoroughly characterize the catalyst prior to plant evaluation, whereas others utilize characterization to explain performance variances. Some new types of catalysts incorporated into this volume include the preparation of novel catalyst supports based on alumina and hydrous titanates. Attrition-resistant catalysts and ultrafine ceramics were prepared by modified spray-drying methods. New catalyst compositions based on vanadium-containing anionic clays were proposed for oxidation. A recently commercialized catalyst based on magnesium spinel was proposed for use in the abatement of sulfur oxide pollutants in fluid... 

In contrast to the structure-catalyst ratio dependence shown in the AIBU3-TiCl4 system, the polymerization of butadiene with a catalyst prepared by reaction of aluminum triethyl or diethylaluminum chloride with vanadium tetrachloride or oxychloride reportedly yields a polymer whose structure is relatively unaffected by the Al/V ratio—i.e., the polybutadiene obtained in heptane at 15° C. contains 95 to 99% tram-1,4-, 0 to 1% cis-1,4-, and 1 to 5% 1,2- structures at Al/V ratios ranging from 0.5 to 10. After extraction with diethyl ether, diisopropyl ether, and benzene, the residual polymer, constituting 55 to 75% of the total polymer, has 99 to 100% tram- 1,4- structure (15). 

To obtain a high yield, it is important to use the right catalyst and the right material for containing the catalyst. With vanadium pentoxide in pyrex tubes, the yield is only 25 percent of the input furfural, but with a vanadium pentoxide/molybdenum trioxide/iron molybdate catalyst in nickel tubes, the yield is in the order of 75 percent. Interestingly, the best yields are obtained when the catalyst, prepared from appropriate ammonium salts, is cured with air at 300 °C in situ, and when it is then used directly at the reaction temperature of 270 °C without allowing it to cool down. 

Vanadium phosphate catalysts are obtained from precursors prepared by a two-step sjmthesis. In the first step, a V0P04-mixed isobutanol-water intercalate was obtained by precipitation from a solution containing vanadyl isobutoxide, H3PO4 and carefully adjusted water content (precursor A). In the second step, precursor B was formed by reflux of precursor A in (i) an inert (n-octane) or (ii) reductive (isobutanol) medium. By such a procedure, precursors and catalysts (with PA atomic ratio equsd to 1.05) displaying widely different structural defects (XRD, IR) were prepared. Catalysts were tested in the oxidation of n-pentane into maleic (AM) and phthalic (PA) anhydrides. Formation of PA demands a highly ordered structure, while AM could be formed on a highly defective VPO catalyst. 

The oxidation of SOi to sulfuric acid, SOt + H2O + 0.5 O2 H2SO4, is catalyzed by potassium vanadium(V) oxide compounds. A typical catalyst preparation sequence involves impregnation of a silica support with a solution containing potassium vanadate (K/V = 3), followed by drying and subsequent calcination at 500°C in air. Under typical operating conditions in SO2/O2/SO3 atmospheres at 400-500°C, the catalytically active species is molten and forms a thin liquid film on the silica. support. As such the. system functions like a bulk oxide catalyst under operating conditions, and the silica mostly serves as a mechanical support medium. 

Vanadium-containing mesoporous silica with highly dispersed and tetrahedrally coordinated V-oxide species ( 04) has been prepared by a modified surfactant templating method [127]. This catalyst shows high photocatalytic activity (X > 300 nm) even in water, while other V-containing silica catalysts, prepared by impregnation or conventional templating methods, have no activity in the presence of water due to hydrolysis of the V 04 species. Retention of activity in water is due to the fact that V 04 species are confined within the silica layer and not exposed on the surface. Despite its confined structure, this photocatalyst is able to oxidize cyclohexane mainly to its alcohol and ketone with only traces of CO2. 

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