Sulfate hydrogenation catalysts

Hydrogenation. Hydrogenation is one of the oldest and most widely used appHcations for supported catalysts, and much has been written in this field (55—57). Metals useflil in hydrogenation include cobalt, copper, nickel, palladium, platinum, rhenium, rhodium, mthenium, and silver, and there are numerous catalysts available for various specific appHcations. Most hydrogenation catalysts rely on extremely fine dispersions of the active metal on activated carbon, alumina, siHca-alumina, 2eoHtes, kieselguhr, or inert salts, such as barium sulfate. 

Blue tungsten oxide and combiaations thereof (106—113) have been the subject of a number of patents, as have copper(II) fluoborate (114) and alkaH metal or ammonium sulfate-hydrogen sulfate catalysts (115,116). 

Aqueous cyanide effluent containing a little methanol in a 2 m3 open tank was being treated to destroy cyanide by oxidation to cyanate with hydrogen peroxide in the presence of copper sulfate as catalyst. The tank was located in a booth with doors. Addition of copper sulfate (1 g/1) was followed by the peroxide solution (27 1 of 35 wt%), and after the addition was complete an explosion blew off the doors of the booth. This was attributed to formation of a methanol vapour-oxygen mixture above the liquid surface, followed by spontaneous ignition. It seems remotely possible that unstable methyl hydroperoxide may have been involved in the ignition process. 

Chemisorphon of the complexes [Cp MR2], [Cp MR3] or [MR4] (Cp = Cp, Cp M = Zr, Ti, Th R = Me, CH2 Bu, CH2TMS) onto superacidic sulfated zirconia (ZRS , where x refers to activation temperature) [81, 91] and sulfated y-alumina (AIS) [90] afforded active benzene hydrogenation catalysts and ethylene polymer-izahon catalysts. The most active catalyst system for the hydrogenation of benzene (arene Zr = 1.5 1, 25 °C, no solvent, 0.1 MPa H2) was [Cp ZrMe2] -ZRS400, which achieved a TOP of 970 h. The activity of this adsorbate catalyst rivals or exceeds those of the most active heterogeneous arene hydrogenahon catalysts known. The... 

Permethylation of carbohydrates.1 Permethylation of carbohydrates in a solid-liquid system is not possible because of lack of solubility in benzene or methylene chloride. The difficulty can be circumvented by reaction of peracetylated sugars with methyl bromide in C6H6-aqueous NaOH with tetrabutylammonium hydrogen sulfate as catalyst. 

Glycosyiation. The a-anomer of ara-7-deazaguanosine (4) has been prepared by glycosyiation with tetrabutylammonium hydrogen sulfate as catalyst of the pyrimidine I with 2,3,5-tri-O-benzyl-l-bromoarabinofuranose (2). The catalyst equilibrates 2 to a mixture of the a- and /(-anomers the more reactive (i-anomer reacts with I by a SN2-displaccmcnt to give mainly 3. 

Fig. 4 shows the TPR profiles of the fresh and spent catalyst. Curve C shows the desorption of hydrocarbons during reduction of the spent catalyst, formed by reduction of carbonaceous deposits on the catalyst surface. The hydrogen consumption profiles of the catalyst (see Curve A and B) show the two peaks, characteristic of palladium sulfate-based catalysts, with a vanadium oxide reduction peak at approximately 400 K and a sulfate reduction peak at 600 K [11,13,16]. The peak position of the sulfate reduction peak is comparable for both catalysts. For the spent catalyst, however, an additional small hydrogen consumption is observed at 700 K, which coincides with the large peak in the FID signal,... 

G. Larsen, E. Lotero, R. D. Parra, L. M. Petkovic, H. S. Silva, and S. Raghavan, Characterization of palladium supported on sulfated zirconia catalysts by DRIFTS, XAS and n - butane isomerzation reaction in the presence of hydrogen, Appl. Catal A 130, 213-226 (1995). 

Palladium on barium sulfate, Pd/BaS04 Acts as a hydrogenation catalyst for nitriles in the Kiliani-Fischer chain-lengthening reaction of carbohydrates (Section 25.6). 

Oxidation of alcohols. Primary and secondary alcohols can be oxidized to aldehydes and ketones, respectively, by potassium chromate and sulfuric acid in a two-phase system (CHCI3-H2O) in the presence of tetra- -butylammonium hydrogen sulfate as catalyst. The method is particularly useful for oxidation of primary... 

The catalytic hydrogenation of a double bond involves the adsorption of the alkene on a metal surface and the transfer of hydrogen from the surface to the double bond. Typical catalysts are finely divided forms of nickel, platinum or palladium, the latter often supported on an inert carrier such as charcoal or barium sulfate. Hydrogenations are carried out in solution, with the hydrogen at atmospheric or higher pressure. The addition of hydrogen is typically cis and from the less-hindered face of the molecule (e.g. the hydrogenation of a-pinene, 3.1). 

These requirements are fulfilled in a method in which dibromodifluoromethane is reacted with dibromomethane and an alkene in the presence of 60% aqueous potassium hydroxide with tetrabutylammonium hydrogen sulfate as catalyst. ... 

In the liquid phase at room temperature, using alcohol as a solvent and palladium supported on barium sulfate as catalyst, the only products observed from 1-butyne hydrogenation were 1-butene (98%) and n-butane (2%) (57). The gas phase reaction using 0.03% palladium on alumina catalyst gave 1-butene (99.1%), cis- and product distributions were maintained until at least 76% removal of the parent hydrocarbon but isomerization and hydrogenation of the 1-butene occurred after complete removal of the alkyne. Thus, l-butjme must displace 1-butene from the surface before its isomerization can occur, and it must prohibit the re-entry of 1-butene into the reacting surface layer. This represents the operation of a powerful thermodynamic factor. 

For selective oxidations in the carbohydrate field, Heyns and coworkers have investigated the use of platinum catalysts in different forms. For reactions in which further oxidation of the desired product is probable (as, for example, in the oxidation of ketose and pentose derivatives ), a milder catalyst of 5 to 10% platinum on activated carbon is recommended. Care must be taken in the preparation of the catalyst otherwise, it is difficult to obtain catalysts of reproducible activity. The platinum is deposited on the carbon by hydrogenation or by reduction with formaldehyde or hydrazine sulfate. The catalyst prepared through formaldehyde... 

Most feeds contain some olefin as an impurity moreover many sulfated zirconia catalysts contain traces of iron or other transition metal ions that are able to dehydrogenate hutane. In the presence of such sites, the olefin concentration is limited by thermodynamics, i.e a high pressure of H2 leads to a low olefin concentration. That aspect of the reaction mechanism has been proven in independent experiments. The isomerization rate over sulfated zirconia was dramatically lowered by H2. This effect is most pronounced when a small amount of platinum is deposited on the catalyst, so that thermodynamic equilibrium between butane, hydrogen and butene was established. In this way it was found that the isomerization reaction has a reaction order of +1.3 in -butane, hut -1.2 in hydrogen [40, 41]. The byproducts, propane and pentane, are additional evidence that a Cg intermediate is formed in this process. As expected, this kinetics is typical for butane isomerization only in contrast pentane isomerization is mainly a monomolecular process, because for this molecule the protonated cyclopropane ring can be opened without forming a primary carbenium ion [42]. 

Figure 3 Conversion of n-butane at 250°C over unpromoted and Pt promoted sulfated zirconia catalysts. Partial pressure of n-butane = 0.2, partial pressure of hydrogen = 0.8.

Deactivation studies on conventional sulfated zirconia at varying partial pressures of n-butane in helium showed two regions of deactivation as reported in the literature. Reaction studies with hydrogen as the diluent gas led to distinct changes in the two regions of activity. These changes could be rationalized by the presence of two active sites on the catalyst surface. A two active site, elementary step bimolecular reaction model is proposed for n-butane isomerization over optimally hydrated sulfated zirconia catalysts. Experimental data... 

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