Sulfates catalyst appearance

Sulfated catalyst activity was determined with the S02 free feedstream in the absence of water The light-off temperatures reported in Fig 3a for propene oxidation show that sulfation by SO2 induces the same effects on catalyst activity than SO2 in the feedstream in the course of the oxidation reaction (Fig 1b). Thus Pt-Rh catalyst activity is not affected by sulfation while monometallic platinum catalysts are far less active after sulfur storage with 20 ppm SC>2 We must note also that a small inhibiting effect appears after sulfur storage with 4 ppm SO2. 

The most common catalyst for low- and medium-pressure hydrogenation is platinum. Platinum oxide is available from a number of suppliers and is converted to colloidal platinum in situ by hydrogenation. Palladium is another commonly used catalyst and is usually prepared on some inert support such as charcoal, barium sulfate, or calcium carbonate. The procedure for the preparation of these catalysts is given in Organic Syntheses. - A rhodium catalyst appears to be particularly effective in reducing aromatic compounds at low pressure and is available on an alumina support. ... 

Catalysts active in the isomerization of n-butane have been synthesized by depositing sulfate ions on well-crystallized defective cubic structures based on ZrOz. This technique for introduction of sulfates does not result in any significant changes in the bulk properties of zirconium dioxide matrix. Active sulfated catalysts were prepared on the basis of cubic solid solutions of ZrOz with calcium oxide and on the basis of cubic anion-doped ZrOz. The dependence of the catalytic activity on the amount of calcium appeared to have a maximum corresponding to 10 mol.% Ca. Radical cations formed after adsorption of chlorobenzene on activated catalysts have been used as spin probes for detection of strong acceptor sites on the surface of the catalysts and estimation of their concentration. A good correlation has been observed between the presence of such sites on a catalyst surface and its activity in isomerization of n-butane. 

Vanadia doped sulfated Ti-pillared clays were prepared and characterized by BET, XRD, XPS, TPD-NH3 and compared with sulfated Ti-pillared clays and vanadia-doped unsulfated Ti-pillared clays. When sulfated Ti-pillared clay was doped with vanadia, the BET surface areas decrease whereas the diffraction line (001) are not significantly affected. The acidic properties of sulfated catalysts are higher than vanadia doped sulfated samples. The comparison of the activity of the catalysts in the selective catalytic reduction (SCR) of NO by ammonia in presence of oxygen show that vanadia doped sulfated Ti-pillared clay were highly active for the SCR NO. Therefore sulfated Ti-pillared clay appears as a good support for vanadia catalysts for the SCR reaction. 

It was shown by Buriak and Osborn [80] that non-micelle-forming anions improved the enantioselectivity of an imine hydrogenation catalyzed by rhodium complexes in the same way as reverse micelles. Complexation of the sulfate or sulfonate anion with the catalyst appears to be responsible for the enhancement of the enantioselectivity. The very strong dependence of the product chirality on the structure of the anion is discussed. Finally, a long-chain ephedrinium salt 17 as surfactant, should be mentioned. 

Rhenium oxides have been studied as catalyst materials in oxidation reactions of sulfur dioxide to sulfur trioxide, sulfite to sulfate, and nitrite to nitrate. There has been no commercial development in this area. These compounds have also been used as catalysts for reductions, but appear not to have exceptional properties. Rhenium sulfide catalysts have been used for hydrogenations of organic compounds, including benzene and styrene, and for dehydrogenation of alcohols to give aldehydes (qv) and ketones (qv). The significant property of these catalyst systems is that they are not poisoned by sulfur compounds. 

Poisoning of deNOx catalysts by SO2 could also be a problem since diesel fuels contain small amounts of sulfur compounds. Only a few studies deal with this subject [11-13]. It appears from the literature that for Cu catalysts the use of MFI as a support reduces the inhibition by SO2. Support effects also appear in the case of Co since Co/MFI is much less sensitive to SO2 than Co/ferrierite [13]. Since this support effect may be related to acidity, it becomes important, to investigate the influence of SO2 on the properties of Cu catalysts supported on Si02, AI2O3, MFI, BEA and unpromoted or sulfate promot Ti02 and Zr02- These latter have been reported active for deNOx [14]. 

Due to the small amount of SO2 in the feed, sulfation of the catalyst by the charge is very slow, and the effect of sulfur appears clearly only when Ae catalyst is sulfated separately. Dosing of SQ2 onto the solids shows that sulfur is indeed ad rbed at the surface since Cu/TiC>2 retains about 0.4 wt% S and Cu-BEA 0.1 wt% S. It is interesting to notice that the effect of SO2 clearly depends on the type of support. 

Franke [47] undertook a comprehensive electroanalytical study of K2S207 mixtures with K2S04, which is formed by Eqs. (47) and (48) and V2Os, a widely-used oxidation catalyst for S02. Pure pyrosulfate under N2 or air (Fig. 38a,b) shows only the reduction to S02 and sulfate, Eq. (48) (all potentials are vs. Ag/Ag+). When S02 is added, a new reduction and oxidation peak appear (Fig. 38c,d). When the electrolyte was pre-saturated with K2S04 (ca. 4 wt.%) (Fig. 39) the gas composition had no direct effect on the voltammetry. Although the equilibrium for Eq. (49) lies well to the right at this temperature, 400 °C, the kinetics are quite slow in the absence of a catalyst. The equilibrium between pyrosulfate and sulfate, Eq. (47), lies well to the left (K = 2 x 10-6), but will proceed to the right in the absence of S03. Thus, the new peaks are sulfate oxidation, Eq. (43), and S03 reduction to sulfite ... 

Further examples are furnished by the spectra of Figs. 10 and 11. A single pellet of virgin catalyst ( 7 x 10mm) was placed in a cell (Fig. 2) and degassed at room temperature, and spectrum S2 was recorded (the main spectral features are the strong absorptions of the kieselguhr support, but some sulfate absorptions can also be discerned). The catalyst was then exposed to 90 torr of SO2 at room temperature and spectrum was recorded with SO2 in the cell, when new features appeared. 

DBCP on a 1% w/w catalyst, on a mass basis, it appears that sulfite has a stronger effect than nitrate or sulfate, which in turn has a stronger effect than chloride. Similarly, for the reaction of PCE on a 1% w/w Pd/PAC catalyst, the effect of solutes in decreasing order of strength are bisulfide, nitrite, nitrate, sulfate, and chloride. From these results, it is clear that solutes present in the water can affect the reaction kinetics the Schiith results indicate that catalysts can be tailored to minimize the negative effects of solutes on the reaction process. 

Although the forward reaction is favored by increase in pressure, this is not employed in practice since 97 to 99% conversion of sulfur dioxide to sulfur trioxide can be accomplished at the temperature specified here, provided suitable catalysts are used. The first catalyst used for this reaction consisted of finely divided platinum dispersed in asbestos, anhydrous magnesium sulfate, or silica gel. Other catalysts were later discovered. Mixtures of ferric and cupric oxides are useful, but these are less efficient than platinum. Certain mixtures containing vanadium pentoxide (V205) and other compounds of vanadium appear to be as good as or better than platinum. There has been much controversy over the relative merits of platinum and vanadium catalysts, and only time will provide the answer as to which is best. 

Some biomass-derived contaminants, on the other hand, may affect the catalytic processing rate. Ammonium shows significant inhibition calcium may also have an effect. Potassium, though, appears to have too little interaction to be noticeable at the concentrations tested. The common acid anions phosphate, sulfate, and chloride appear to have no effect, while nitrate changes the conversion route and the product slate through a sugar isomerization mechanism. These tests show that while some contaminants may affect the catalytic processing rate, most have no impact, and there is no indication of a combinatorial effect on the catalyst when several of the contaminants are present in the feedstock. Consequently, the calcium and ammonium continue to be the key components of concern. 

The reaction of oxiranes with carbonyl compounds in the presence of Lewis acids is an efficient way of preparing 1,3-dioxolanes (81S501). The reaction, shown in Scheme 33, proceeds with inversion of stereochemistry of the oxirane. A diol does not appear to be an intermediate even in the presence of water. Many Lewis acid catalysts are effective, but the use of anhydrous copper(II) sulfate in an excess of the carbonyl compound as solvent probably offers the mildest conditions. Since the copper(II) sulfate is insoluble, the reaction appears to be truly heterogeneous in nature and the mixture must be well stirred (78JOC438). 

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