Silver oxide, catalyst preparation

Diols are prepared from alkenes by oxidation with reagents such as osmium tetroxide, potassium permanganate, or hydrogen peroxide (Section 11-7C). However, ethylene glycol is made on a commercial scale from oxacy-clopropane, which in turn is made by air oxidation of ethene at high temperatures over a silver oxide catalyst (Section 11-7D). 

The oxidation of inexpensive olefins to maleic anhydride is of economic interest, since apparently it is competitive with the oxidation of benzene to maleic anhydride in some locations. As yet, however, oxidation of C4 hydrocarbons to maleic anhydride has given only about 50 % of the theoretically possible conversion to the desired product. Bretton, Wan, and Dodge 12) examined the oxidation of several C4 olefins over silver and silver oxide catalysts, but found only traces of products other than COg and HgO. With a vanadium catalyst prepared by decomposition of ammonium metavanadate on low-area alumina, substantial yields of intermediate products were found. Longfield and Dixon 57) and Matsumoto and co-workers 156) reported similar results a summary is given in Table XIV. These reactions were usually... 

Many low molecular weight aldehydes and ketones are important industrial chem icals Formaldehyde a starting material for a number of plastics is prepared by oxida tion of methanol over a silver or iron oxide/molybdenum oxide catalyst at elevated temperature... 

Salts of neodecanoic acid have been used in the preparation of supported catalysts, such as silver neodecanoate for the preparation of ethylene oxide catalysts (119), and the nickel soap in the preparation of a hydrogenation catalyst (120). Metal neodecanoates, such as magnesium, lead, calcium, and zinc, are used to improve the adherence of plasticized poly(vinyl butyral) sheet to safety glass in car windshields (121). Platinum complexes using neodecanoic acid have been studied for antitumor activity (122). Neodecanoic acid and its esters are used in cosmetics as emoUients, emulsifiers, and solubilizers (77,123,124). Zinc or copper salts of neoacids are used as preservatives for wood (125). 

The silver catalyst was prepared by reducing silver oxide. The silver oxide used was prepared by adding a solution of potasium hydroxide to an aqueous solution of silver nitrate. A small amount of 0.3% K SO solution was added to the silver oxide powder as a promoter and, after mixing, was dried at 105°C for 24hr in a dark room. This was coated on a-A O of 20-42 mesh in the presence of a small amount of ethanol until the sample reached a size of 12-14 mesh. After the ethanol in the silver oxide powder had been completely vaporized in air at room temperature, the sample was reduced in a reactor with a flow of for 12 hr at 50°C and successively for 12 hr at 100°C. The composition of the catalyst so prepared was 206.0 g-Ag, 1.132 g-K S0 / 5 3.5 g-A O. The BET surface area was 0.3 m / g-A.g. HThe constant activity of this catalyst was obtained by flowing the mixture of 5% C H, 20% 0 and 75% He at 91°C for 48 hr. 1... 

In this part, we prepared and studied the Ag/Si02 catalyst by one-step and two-step sol-gel methods. The results show that the Ag/Si02 catalyst prepared here is one kind of bulk material which has a high surface area. The Ag/Si02 catalyst is made up with functional component of Ag or silver oxide in 20 to 30 nm and carrier Si02. Moreover, we found that the different preparation methods have great effect on crystal structure of the samples. The structure of the sample prepared by the one-step method is always a single crystal structure. And the structure of the sample prepared by the two-step method is always a mixed crystal structure. 

In support of the conclusion based on silver, series of 0.2, 0.5, 1.0, 2.0, and 5.0 % w/w of platinum, iridium, and Pt-Ir bimetallic catalysts were prepared on alumina by the HTAD process. XRD analysis of these materials showed no reflections for the metals or their oxides. These data suggest that compositions of this type may be generally useful for the preparation of metal supported oxidation catalysts where dispersion and dispersion maintenance is important. That the metal component is accessible for catalysis was demonstrated by the observation that they were all facile dehydrogenation catalysts for methylcyclohexane, without hydrogenolysis. It is speculated that the aerosol technique may permit the direct, general synthesis of bimetallic, alloy catalysts not otherwise possible to synthesize. This is due to the fact that the precursors are ideal solutions and the synthesis time is around 3 seconds in the heated zone. 

The search for a new epoxidation method that would be appropriate for organic synthesis should also, preferably, opt for a catalytic process. Industry has shown the way. It resorts to catalysis for epoxidations of olefins into key intermediates, such as ethylene oxide and propylene oxide. The former is prepared from ethylene and dioxygen with silver oxide supported on alumina as the catalyst, at 270°C (15-16). The latter is prepared from propylene and an alkyl hydroperoxide, with homogeneous catalysis by molybdenum comp e ts( 17) or better (with respect both to conversion and to selectivity) with an heterogeneous Ti(IV) catalyst (18), Mixtures of ethylene and propylene can be epoxidized too (19) by ten-butylhydroperoxide (20) (hereafter referred to as TBHP). 

In support of that explanation, X-ray analysis of the catalyst after use indicated the presence of MgO. Hence, the catalytically active phase was finely divided copper in intimate contact with magnesia, quasi as carrier. The same phenomenon was observed with the Zintl-phase alloys of silver and magnesium. Such catalysts were then deliberately prepared by coprecipitation of copper and silver oxides with magnesium hydroxide, followed by dehydration and reduction. Table I shows that these supported catalysts had the same activation energies as those formed by in situ decomposition of copper and silver alloys with magnesium. 

Thus, Hickinbottom17 was able to prepare methyl a-D-glucopyranoside (in approximately 70% yield) by reaction of 3,4,6-tri-0-acetyl-2-0-tri-chloroacetyl-/3-D-glucosyl chloride in methanol, with silver oxide as catalyst and acceptor for hydrogen chloride. 

The silver catalyst used was prepared from silver oxide by the same procedure as the catalyst used for ethylene oxidation [8J, which contained a small amount of K2S0<, as a promoter and supported on ct-Al203 of 20-40 mesh. The composition of this sample was 154g-Ag,... 

Ethylene oxide is prepared industrially by the vapor phase oxidation of ethylene over a supported silver catalyst at elevated temperatures.49la c Application of this reaction to higher olefins results in complete oxidation of the olefin to carbon dioxide and water. In general, autoxidations of olefins are notoriously unselective because of the many competing reactions of the intermediate peroxy radicals in these systems. 

Oxidative demethylation. Both silver(II) oxide (4,431-432) and CAN (7,55) have been used for oxidative demethylation of dimethyl ethers of 1,4-hydroquinones to give p-quinones. A direct comparison of the two reagents indicates that yields are higher with CAN. With either reagent, yields are improved when the N-oxide of pyridine-2,6-dicarboxylic acid is added as catalyst. The oxide is prepared by oxidation of pyridine-2,6-dicarboxylic acid with H2O2 and Na2S04. ... 

Preparation of diazoketones and their rearrangements during hydrolysis (method 271) and alcoholysis (method 295) are discussed elsewhere. Ammonolysis of diazoketones leads to amides of acids containing one more carbon atom than the original acyl halide. Halogen atoms may be present in a remote position on an aliphatic chain. The reaction is carried out by heating the diazoketone in alcohol or dioxane solution with aqueous ammonia in the presence of silver oxide or silver nitrate catalysts. Substituted acetanilides are formed when aniline is used in place of ammonia. ... 

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