Reduction procedures, ammonia catalyst

The method of reduction influences the properties of ammonia catalysts. A generally appropriate reduction schedule cannot be prescribed because different types of catalysts call for different reduction procedures to reach their most active state. It has previously been mentioned that the promoters used in ammonia catalysts have a retarding effect on the reduction. According to the author s experience, oxides of the alkaline earth metals, especially CaO, make the catalysts especially difficult to reduce. As will be remembered these oxides enter the magnetite matrix readily. 

The preparation of Ru supported catalysts by sol-gel method, indeed, was extended to obtain new formulations by changing the type of support. Alkali-promoted Ru/MgO systems were prepared starting from magnesium ethoxide, Ru3(CO)i2 and a cesium compound [9]. The gels were subjected to an activation/reduction procedure to substantially obtain Ru-CsOH/MgO and then tested as catalysts in the ammonia synthesis at atmospheric pressure. It was evidenced that the sol-gel prepared Cs-promoted Ru/MgO catalysts are much more active, under similar reaction comlitions, than the analogous catalysts prepared by the impregnation procedures reported in literature [10]. 

Different reduction procedures apply if the catalyst is prereduced or when a combination of prereduced and unreduced catalyst is used. Whereas reduction of the bulk magnetite catalyst goes on over days, the reduction of the superficial oxidic layer of the prereduced catalyst is facile and may be accomplished within approximately one day if solely prereduced catalyst is charged. Often the first bed is charged with prereduced catalyst to enable fast reduction and onset of the ammonia synthesis reaction, which thereby liberates heat to support the endothermic reduction in the remaining part of the bed. 

The 17-ethylene ketal of androsta-l,4-diene-3,17-dione is reduced to the 17-ethylene ketal of androst-4-en-3,17-dione in about 75% yield (66% if the product is recrystallized) under the conditions of Procedure 8a (section V). However, metal-ammonia reduction probably is no longer the method of choice for converting 1,4-dien-3-ones to 4-en-3-ones or for preparing 5-en-3-ones (from 4,6-dien-3-ones). The reduction of 1,4-dien-3-ones to 4-en-3-ones appears to be effected most conveniently by hydrogenation in the presence of triphenylphosphine rhodium halide catalysts. Steroidal 5-en-3-ones are best prepared by base catalyzed deconjugation of 4-en-3-ones. ... 

For ammonia and primary amines there are two possible pathways, but when secondary amines are involved, only the hydrogenolysis pathway is possible. Other reducing agents167 can be used instead of hydrogen and a catalyst, among them zinc and HCI, sodium cyano-borohydride NaBHjCN,168 sodium triacetoxyborohydride,169 sodium borohydride,170 iron pentacarbonyl and alcoholic KOH,171 BH -pyridine,172 and formic acid. When the last is used, the process is called the Wallach reaction. In the particular case where primary or secondary amines are reductively methylated with formaldehyde and formic acid, the method is called the Eschweiler-Clarke procedure. It is possible to use ammonium (or amine) salts of formic acid,173 or formamides, as a substitute for the Wallach conditions. This method is called the Leuckart reaction, and in this case the products obtained are often the N-formyl derivatives of the amines instead of the free amines. Primary and secondary amines can be N-ethylated (e.g., ArNHR —< ArNREt) by treatment with NaBH4 in acetic acid.175... 

On a small scale, cracking ammonia can produce hydrogen for reduction. Transport and storage of hydrogen as ammonia is compact, and the cracking procedure involves only a hot pipe packed with catalyst and... 

Benzene and aikyibenzenes are quantitatively converted to cyclohexanes by catalytic hydrogenation. Modem procedures employ liquid-phase hydrogenation over nickel catalysts at 100-200° or over platinum catalysts at room temperature. Nickel catalysts are poisoned by traces of thiophene and water. Small quantities of hydrogen halide increase the effectiveness of platinum catalysts. Isomerization occurs during the reduction of benzene over nickel at 170° the cyclohexane formed is probably contaminated with methylcyclopentane, Partial reduction of benzene to 1,4-dihydrobenzene is accomplished by sodium in liquid ammonia at —45°. ... 

Procedures involving the reduction of oxirane and ammonia in the vapor phase over an Al203-Si02 catalyst have been patented for the preparation of pyrazine, piperazine, and morpholine. The formation of quinoxalines is illustrated in Eq. 225. ... 

Numerous variations to the classical Kjeldahl procedure, such as various digestion catalysts and various methods of determinations of ammonia, have been proposed and are summarized in the reviews of Ma et al. (1982). To determine nitrogen in compounds containing N—N, N=N, NO, and NO2, modifications such as zinc iron reduction must be made to the usual procedure (Styermark, 1961). Certain forms of nitrogen such as triazoles cannot be determined by the Kjeldahl method. 

Iron-zeolite catalysts present an important type of materials with broad application for selective oxidations (i.e. benzene hydroxylation) and environmentally important processes, like SCR reduction of NOx or N2O decomposition. In the case of SCR reaction they could provide a convenient substitution of the vanadia-based system using environmentally problematic ammonia, by more convenient paraffin as a reducing agent. Unfortunately, the efficiency in utilization of paraffin is inferior in comparison to ammonia, namely due to paraffin nonselective oxidation by oxygen catalyzed by unspecified iron-oxide type species typically present in the iron-zeolite catalysts. The mostly used preparation processes include impregnation from water solutions, ion exchange procedures, both in water solution or solid state, as well as gas phase CVD. 

As these alkaloids are not only used in chemistry as chiral auxiliaries, starting materials, and catalysts, but also in medicine, so technical syntheses have been developed and all of these compounds are commercially available. The standard materials ( )-(l/ ,2,S )-ephedrine [(-)-3) and ( —)-(lff,25,)-norephedrine [(-)- ] are produced in a technical process on multikilogram scale by reductive amination (with methylamine or ammonia, respectively) of (—)-(f )-l -hydroxy- Tphenyl-2-acetone with a platinum catalyst1. The ketone is in turn obtained by a biotechnological procedure from cultures of selected yeast strains (Saccharomyces sp.)2. 

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