Raney-metal catalysts

Dry reduced nickel catalyst protected by fat is the most common catalyst for the hydrogenation of fatty acids. The composition of this type of catalyst is about 25% nickel, 25% inert carrier, and 50% soHd fat. Manufacturers of this catalyst include Calsicat (Mallinckrodt), Harshaw (Engelhard), United Catalysts (Sud Chemie), and Unichema. Other catalysts that stiH have some place in fatty acid hydrogenation are so-called wet reduced nickel catalysts (formate catalysts), Raney nickel catalysts, and precious metal catalysts, primarily palladium on carbon. The spent nickel catalysts are usually sent to a broker who seUs them for recovery of nickel value. Spent palladium catalysts are usually returned to the catalyst suppHer for credit of palladium value. 

To accelerate the polymerization process, some water-soluble salts of heavy metals (Fe, Co, Ni, Pb) are added to the reaction system (0.01-1% with respect to the monomer mass). These additions facilitate the reaction heat removal and allow the reaction to be carried out at lower temperatures. To reduce the coagulate formation and deposits of polymers on the reactor walls, the additions of water-soluble salts (borates, phosphates, and silicates of alkali metals) are introduced into the reaction mixture. The residual monomer content in the emulsion can be decreased by hydrogenizing the double bond in the presence of catalysts (Raney Ni, and salts of Ru, Co, Fe, Pd, Pt, Ir, Ro, and Co on alumina). The same purpose can be achieved by adding amidase to the emulsion. 

Probably the largest use of Ni is in the manuf of Monel metal, stainless steels, Ni-chrome resistance wire, in alloys for electronic and space applications, and as a catalyst (Raney Ni). It is also used as a fuel in pyrotechnics (Ref 2) and... 

A significant volume of literature relates to our work. Concerning choice of support, Montassier et al. have examined silica-supported catalysts with Pt, Co, Rh Ru and Ir catalysts.However, these systems are not stable to hydrothermal conditions. Carbon offers a stable support option. However, the prior art with respect to carbon-supported catalysts has generally focused on Ru and Pt as metals.Additionally, unsupported catalysts have also been reported effective including Raney metals (metal sponges).Although the bulk of the literature is based on mono-metallic systems, Maris et al. recently reported on bimetallic carbon-supported catalysts with Pt/Ru and Au/Ru. In contrast, our work focuses primarily on the development of a class of rhenium-based carbon supported catalysts that have demonstrated performance equal to or better than much of the prior art. A proposed reaction mechartism is shown in Figure 34.2 °l... 

It is noteworthy that the relative proportion of amine 44 and bicumyl (43) which reflects the ratio of the rate of electronation to the rate of reaction with M(H) (the competition between electronation and reaction with M(H)), varies with the Raney metal (compare entries 1 and 3 of Table 1, and entries 2 and 4) and with the electrode potential (compare entries 1 and 2). The more negative is the potential, the faster is the rate of electronation and the higher should be the proportion of bicumyl (43) as observed (entries 1 and 2). The less active the Raney metal as hydrogenation catalyst, the slower is the rate of reaction with M(H) (the lower is the amount of M(H) at the surface of the electrode) and the lower is the amount of aminocumene (44). RCu is the least active catalyst and the proportion of aminocumene (44) is indeed the lowest at the RCu cathode (entry 4). 

The hydrogenation of HMF in the presence of metal catalysts (Raney nickel, supported platinum metals, copper chromite) leads to quantitative amounts of 2,5-bis(hydroxymethyl)furan used in the manufacture of polyurethanes, or 2,5-bis(hydroxymethyl)tetrahydrofuran that can be used in the preparation of polyesters [30]. The oxidation of HMF is used to prepare 5-formylfuran-2-carboxylic acid, and furan-2,5-dicarboxylic acid (a potential substitute of terephthalic acid). Oxidation by air on platinum catalysts leads quantitatively to the diacid. [32], The oxidation of HMF to dialdehyde was achieved at 90 °C with air as oxidizing in the presence of V205/Ti02 catalysts with a selectivity up to 95% at 90% conversion [33]. 

Aldehydes and ketones are reduced to 1° and 2° alcohols, respectively, by hydrogenation with metal catalysts (Raney nickel, Pd—C and Pt02). They are also reduced to alcohols relatively easily with mild reducing agent, e.g. NaBH4, or powerful reducing agent, e.g. LiAlILj. The key step in the reduction is the reaction of hydride with the carbonyl carbon. 

Despite the large amount of data collected in this field, options seem to be restricted to coatings containing Ni or Co, and Mo, with some additives apparently necessary to impart the wanted properties. It follows that the problem of cathode activation is only in part a question of synergism, while the microscopic structure of the catalyst appears to be of greater importance. Thus, Raney Ni still stands out in the group of possible catalysts [110, 531]. The role of Al (or Zn) does not seem to be simply that of sacrificial components. Residual Al present in the structure plays probably a role which can be similar to that of Cd in Ni-Mo. For this reason mixed Raney metals show great promise [415]. Raney Ni-Co (10%) exhibit a very extended... 

In the case of catalytic dense membranes such as palladium alloy sheets or tubes, a smooth membrane surface suffers from a small active surface area per unit volume of catalyst. This drawback can be remedied to some extent by adopting some conventional catalyst preparation methods to roughen the membrane suiface(s) to ensure that only the region near the surface is affected unlike the Raney metal catalysts where the entire matrix is leached. For example, Gryaznov [1992] suggested the use of thermal diffusion of a chemically active metal into a Pd alloy sheet followed by acid treatment to remove this metal. 

Hydrogenolysis of epoxides to yield alcohols has been much reported in the patent literature, because of its importance as an industrial process, but studies on reactivity and selectivity have not been done systematically. The selectivity is highly dependent on the substituents, as in the case of reduction using metal hydrides. As a metal catalyst, Raney Ni was intensively examined in the early stage. It usually requires high pressures (ca. 100 atm) and temperatures (100 C), as shown in Table 10. Alcohols, benzene, THF and even water have been used as solvents. Accordingly, a hydroxy group in the epoxides remains intact, and hydrocarbons are formed only as by-products. In some cases by-product formation can... 

Like Raney metals, the traditional iron-based catalyst for ammonia synthesis, Eq. (7), contains only low levels of promoters, and the operating catalyst is effectively metal. 

Other specialized alloys have also been used to prepare skeletal metal catalysts. Raney ruthenium has been prepared from the ruthenium aluminum alloy. 20 A colloidal platinum has been prepared by the action of acetic acid on a platinum lithium alloy. l Skeletal nickel catalysts have been made from a number of intermetallic compounds of nickel with the rare earth elements, lanthanum and samarium. The rare earth element is removed from the alloy by reaction with diiodoethane or dibromoethane which convert the rare earths to the soluble halide salts. 22 Several multicomponent catalysts have also been prepared from the corresponding aluminum alloys. 23-126... 

In previous studies the authors have reported that metals oxides such as GaaOa, AI2O3, Zr02 and Cr203 contained in Cu/ZnO-based catalysts have an important role to improve simultaneously the activity and the selectivity[1, 2]. Unlike Cu/ZnO-based catalysts, Raney copper catalysts have not been widely reported in the literature as practical catalysts for methanol synthesis. However, 20 years ago Wainwright and co-workers have been the first to report the potentiel use of Raney Cu and Raney Cu-Zn as catalysts to produce methanol from syngas to use as synthetic liquid fuel [3]. Recent works of Wainwright et al. on methanol synthesis... 

Type of catalyst noble metals are usually supported on a carrier sometimes they are used as fine powders (Pd black and Pt black, Pt02), Ni is most often applied as skeletal Raney nickel or supported on sUica Cu is used as Cu-chromite. 

The difficulty of thermal treatment of slurry-phase catalysts has resulted in the predominant use of Raney metals and precious metals in the fine-chemical industry. Raney metals are produced from an aluminum alloy of the metal to be used as a catalytically active component. Treatment with alkali leaches aluminum from the alloy and leaves a very finely divided metal [10] as ca 10 to 20 nm metal particles clustered into conglomerates of several microns. Aluminum remaining in the metal after treatment with alkali protects the metal against oxidation. The aluminum reacts very slowly with the water in which the Raney metals are stored and... 

Raney metals are attractive because thermal treatment in a gas flow is not required to produce the catalytically active metal. Storage of the pyrophoric catalyst is, moreover, easy, because the catalyst can be stored in water. Another important advantage is that the catalyst particles are heavy, which enables separation of the catalyst by settling and decantation. A final attractive feature of Raney metals is that they can be exposed to alkaline liquids. Many other metal catalysts are not stable in alkaline liquids. Most well known is Raney nickel, which is an attractive hydrogenation catalyst [11-20]. Raney copper and Raney cobalt are also frequently employed. Raney metals are mostly used for hydrogenations in the fine-chemical industry. Raney nickel and Raney cobalt often have different selectivity the reason for the difference between nickel and cobalt is often obscure, though cobalt is more liable to poisoning and oxidation. 

Raney metals and supported precious metal catalysts are very easy to employ in the fine-chemical industry. The application of promoters with Raney metals and stabilization by metallic aluminum remaining in the catalyst call for more fundamental investigations. Research on the initial aluminum alloy calls for experience in metallurgy, which is usually not available in laboratories dealing with solid catalysts. 

With supported catalysts in particular the catalytically active surface is much smaller than the total surface area, because the surface area of the support is usually much larger than the active surface area. With non-supported catalysts, such as Raney metals, it is, however, also highly important to compare the total surface area with the active surface area to assess whether residual alumina covers a significant fraction of the metal surface. Therefore separate measurements of total surface area and catalytically active surface area are required. 

Although palladium occupies the dominant position in semi-hydrogenation catalysts, it is by no means the only metal suitable for formulation into a viable catalyst. Mention has already been made of the nickel boride alternatives, with or without copper promotion, for example. Other examples include the skeletal catalyst Raney nickel [69], alumina-supported nickel [70], and aluminum phosphate-supported nickel [71] (Eqs 21 and 22) ... 

The activated Raney metal slurry catalysts (W. R. Grace Co.) enployed in this study were primarily Ni and Co. Ra 2800 contains only Ni and Ra 2400 contains nickel along with chrome and iron promoters. Ra 2724 contains cobalt promoted with chrome and iron. 

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