Raney nickel catalysts properties

Oxiranes react with a wide variety of nucleophilic reagents, under neutral or base- or acid-catalyzed conditions, and this property has led to their extensive exploitation in synthesis. They also undergo hydrogenation in the presence of Raney nickel catalyst, which,... 

The introduction of further alloying components into a Ni2A1 alloy had a substantial effect on the properties of the Raney nickel catalyst. 

The modification of the Ni Al alloy by addition of molybdenum or chromium has a significant effect on the properties of the Raney nickel catalyst in the reaction of hydrogenation of valeronitrile. In the case of molybdenum, the catalytic properties may be correlated to the physico-chemical characteristics of the catalysts. Chromium is an effective promoter for initial activity and for selectivity. The mechanism for promotion of chromium in Raney nickel is not known exactly. 

Secondary amines can be prepared from the primary amine and carbonyl compounds by way of the reduction of the derived Schiff bases, with or without the isolation of these intermediates. This procedure represents one aspect of the general method of reductive alkylation discussed in Section 5.16.3, p. 776. With aromatic primary amines and aromatic aldehydes the Schiff bases are usually readily isolable in the crystalline state and can then be subsequently subjected to a suitable reduction procedure, often by hydrogenation over a Raney nickel catalyst at moderate temperatures and pressures. A convenient procedure, which is illustrated in Expt 6.58, uses sodium borohydride in methanol, a reagent which owing to its selective reducing properties (Section 5.4.1, p. 519) does not affect other reducible functional groups (particularly the nitro group) which may be present in the Schiff base contrast the use of sodium borohydride in the presence of palladium-on-carbon, p. 894. 

Surface area, pore size, and pore volume are among the most fundamentally important properties in catalysis because the active sites are present or dispersed throughout the internal surface through which reactants and products are transported. The pores are usually formed by drying or calcining precipitates of hydrous oxides however, some materials possess porosity naturally, as in the case of carbons, natural zeolites, and others. Raney nickel catalysts... 

The hydrogenation reaction takes place in the presence of a Raney nickel catalyst at 120-150°C (250-300°F) and 5000 psig. Nylon properties are sensitive to impurities in the feedstock so the reaction and purification steps for both adiponitrile and hexamethylene diamine are carried out to minimize by-products and impurities in the HMDA product. The hydrogenation of adiponitrile is carried out in a large quantity of ammonia which prevents the formation of hexamethyleneimine by-product. Ammonia also acts as a heat transfer fluid and helps maintain the reaction temperature. The conversion of adiponitrile is nearly 100% and the selectivity to HMDA is 97% giving an overall yield of HMDA from adiponitrile of 96.7%. 

Physicochemical properties (metallic surface area, total surface area) of Raney Nickel catalysts prepared from well defined precursor alloys were related to the metallurgical structures of these alloys. The microstructure of the catalysts was correlated with the physicochemical characteristics and their activities for hydrogenation of acetophenone in the liquid phase. 

Although Raney catalysts have been used for a long time, the knowledge of the Influence of the metallurgical structure of the precursor alloy upon catalytic properties is limited. Moreover, catalytic properties can be strongly modified by metallic addition (2-4). This work is part of a systematic study on the influence of metallurgical parameters on the catalytic properties of doped and undoped Raney Nickel catalysts. 

Experiment HGR-13. A 2-ft bed of commercial catalyst was tested as a packed bed of 0.25-in. pellets (see Table I for bed properties). This test was similar to experiment HGR-14 in which the catalyst bed consisted of parallel plates sprayed with Raney nickel. The experiment was... 

During water storage slow oxidation takes place. In particular the most active Raney catalysts show. severe deactivation (they should not be stored more than a few weeks). Other types of catalysts though less active are much more stable. In fine chemistry activity is often not the most important catalytic property. This certainly holds for Raney nickel. On a nickel... 

Supported Co, Ni, Ru, Rh, Pd and Pt as well as Raney Ni and Co catalysts were used for the hydrogenation of dodecanenitrile to amines in stirred SS autoclaves both in cyclohexane and without a solvent. The reaction temperature and the hydrogen pressure were varied between 90-140 °C and 10-80 bar, respectively. Over Ni catalysts NH3 and/or a base modifier suppressed the formation of secondary amine. High selectivity (93-98 %) to primary amine was obtained on Raney nickel, Ni/Al203 and Ru/A1203 catalysts at complete nitrile conversion. With respect to the effect of metal supported on alumina the selectivity of dodecylamine decreased in the order Co Ni Ru>Rh>Pd>Pt. The difference between Group VIII metals in selectivity can be explained by the electronic properties of d-band of metals. High selectivity to primary amine was achieved on base modified Raney Ni even in the absence of NH3. 

The modification of the Raney nickel with low Mo amount (x = 0.05 or 0.1) lead to catalysts which had roughly the same kinetic behaviour as the undoped. Further introduction of molybdenum in the Ni A13 alloy had a substantial negative effect on the properties of the catalysts, with a drop in the... 

The observation that no hydrogenolysis of the C-X bond takes place as long as either nitro compounds or reaction intermediates are present can be explained by the strong adsorption of these molecules, thereby preventing the interaction of the C-Cl bond with the catalyst. The mode of action of the modifiers is less clear. It could be due to a modification of the catalytic properties of the Raney nickel or also to a competitive adsorption between the effective modifiers and the... 

There have been a considerable number of papers reporting the properties of sulphur-resistant methanation catalysts, i.e., catalysts which can operate successfully in significant partial pressures of H2S. Most of these report work using catalysts containing vanadium, molybdenum, and such metals. However, attempts have been made to find nickel-based catalysts containing suitable additives to allow them to operate in such atmospheres. For example, Bartholomew and Uken115 have compared the deactivation behaviour of a range of nickel catalysts in 10 p.p.m. H2S. They found that nickel boride catalysts and Raney nickel materials deactivated more slowly than did unsupported nickel and alumina-supported nickel. They attributed this improvement to two factors ... 

Following the development of sponge-metal nickel catalysts by alkali leaching of Ni-Al alloys by Raney, other alloy systems were considered. These include iron [4], cobalt [5], copper [6], platinum [7], ruthenium [8], and palladium [9]. Small amounts of a third metal such as chromium [10], molybdenum [11], or zinc [12] have been added to the binary alloy to promote catalyst activity. The two most common skeletal metal catalysts currently in use are nickel and copper in unpromoted or promoted forms. Skeletal copper is less active and more selective than skeletal nickel in hydrogenation reactions. It also finds use in the selective hydrolysis of nitriles [13]. This chapter is therefore mainly concerned with the preparation, properties and applications of promoted and unpromoted skeletal nickel and skeletal copper catalysts which are produced by the selective leaching of aluminum from binary or ternary alloys. 

The term major active component may be used to describe the active component, the proportion of which greatly exceeds that of the others. Secondary components added on purpose may be described as additives, whereas the term impurities should be reserved for trace amounts of other elements, over which the investigator (manufacturer) has little control. The use of the word promoter implies that the additive improves some particular property of the catalysts, and it is desirable to indicate this property when known (e.g. activity, selectivity, textural properties, resistance to sintering). The term modifier is used sometimes in this context, but is not recommended. The term modifier is used in a special and proper sense in the context of asymmetric hydrogenation when, for example, Raney nickel is modified by optically active tartaric acid in order to impart the property of asymmetry to hydrogenation reactions over the catalyst. 

In 1925 Murray Raney (la) was granted a patent covering a new method of preparation of a nickel catalyst. A pulverized nickel-silicon alloy was reacted with aqueous sodium hydroxide to produce a pyrophoric, brownish nickel residue with superior catalytic properties. Upon investigation of other alloys of nickel and alkali-soluble metals, it was found that the aluminum alloy could be made with ease (lb) and was easily pulverized. The catalyst which is prepared by the action of aqueous sodium hydroxide on this nickel-aluminum alloy is known as... 

Studies of the mechanism of catalytic hydrogenation [42] are complicated by its heterogeneous character, for the reaction is highly sensitive to variations in the surface properties of the catalyst. Most steroid hydrogenations are performed on palladium, platinum, or Raney nickel, although other metals have been used. Interpretations of mechanism are stiU based upon the suggestion by Horiuti and Polanyi [43] 1934 that the... 

Raney-type nickel catalysts are typically prepared by leaching aluminium from a Ni-Al alloy using a concentrated sodium hydroxide solution [1-3], This process of activation critically affects the structure and properties of Raney-type nickel catalysts. The initial structure and composition of the starting alloy also influence the performance of the final catalyst [4-7], In this paper, numerical modelling is compared to experimental measurements in an attempt to simulate both the 3D morphology of as-leached Raney-Ni catalyst material and investigate the nature of the exposed catalyst surfaces. 

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