Skeletal Nickel Catalysts

Table 5.2 Effect of Promoters on the Activity of Skeletal Nickel Catalysts for Hydrogenation of Different Functional Groups...

Surface modification of skeletal nickel with tartaric acid produced catalysts capable of enantiose-lective hydrogenation [85-89], The modification was carried out after the formation of the skeletal nickel catalyst and involved adsorption of tartaric acid on the surface of the nickel. Reaction conditions strongly influenced the enantioselectivity of the catalyst. Both Ni° and Ni2+ have been detected on the modified surface [89]. This technique has already been expanded to other modified skeletal catalysts for example, modification with oxazaborolidine compounds for reduction of ketones to chiral alcohols [90],... 

When the hydrochloride salt of 2,3,4,4a,5,6-hexahydro-l//-pyridazino [1,6-a]quinoline was subjected to catalytic hydrogenation in ethanol over Pt02, 3-[2-(l,2,3,4-tetrahydroquinolyl)]propylamine was obtained (66YZ608). Catalytic reduction of perhydropyrido[l,2-ft]pyridazine over a skeletal nickel catalyst in ethanol at 30 atm gave ring-opened 2-(3-aminopropyl)piperidine (66KGS91). 

REDUCTIVE AMINATION OF ACETONE DN TIN MODIFIED SKELETAL NICKEL CATALYSTS... 

In this work results obtained in a case study, i.e. the reductive amination of acetone on a skeletal nickel catalyst to isopropylamine and diisopropylamine will be given and discussed. Reactions involved in the reductive amination of acetone are given in ... 

It is known that upon distillation of the reaction mixture of the reductive amination of acetone diisopropylamine and isopropanol forms a binary azeotrope making the separation extremely difficult. Therefore, the goal of this work was to find the modes and ways for the suppression of the formation of isopropanol via selec tive poisoning the skeletal nickel catalyst by a second metal such as tin. 

Granular skeletal nickel catalyst with particle size of d = 3-5 mm was prepared by leaching a Ni-Al alloy containing 5D wt% nickel. Half of the amount of aluminium was leached out with 3 wt% NaOH-water solution at 50°C for 12 hours. After leaching the catalyst was washed with distilled water and was kept under an aqueous solution having pH = 9. 

In this series of experiments the reactivity of hydrogen chemisorbed on granular skeletal nickel catalyst towards different tin alkyl compounds, i.e. SnEt, SnBu, SnEt Cl and SnBz2Cl2 [Et =... 

Fig. 1. Relationship between selectivities and H2/NH3 molar ratio in the reductive amination of acetone on uninuUified skeletal nickel catalyst (T = i ilV., P = 0.0 MPa, WHSV = 0.0 h 1, NH3/AC = 2).

Data given in Table 2. indicated that upon increasing the reaction temperature in the reductive amination of acetone the selectivity towards DIPA especially on tin modified catalysts significantly increased, whereas selectivitiss towards other prodocts decreased in different extent. Such an increase in the selectivity of formation of DIPA upon increasing the reaction temperature can not be explained by thermodynamics LlA], and it has not been observed n conventional skeletal nickel catalysts [2, 14 ]. Therefore, it is suggested that the enhanced selectivity towards OIPA obtained at 19D-20G°C can be attributed to the high A10(0H) content of the catalyst l2]. However, the mechanism of the formation of the secondary amine requires further elucidation. 

The selectivity pattern of catalysts prepared by using SnEt2Cl2 showed that the IPA/0IPA ratio has increased compared to that obtained on catalysts modified by tin tetraalkyls. Dn catalysts iMi-Snht-.lll., the selectivity of the formation of isopropanol decreased to. .. A - -..I.. Upon introducing tin from SnBz Cl the activity of the skeletal nickel catalyst slightly decreased. On this modified... 

It has been demonstrated that skeletal nickel catalysts can be modified with tin by using CSRs taking place between tin alkyls and hydrogen adsorbed on nickel. Upon applying this type of modification the selectivity pattern of the catalysts in the reductive ami-nation of acetone can be tailored. Selective poisoning of sites responsible for the formation of isopropanol could be achieved by using tin dibenzyl (or diethyl] dichloride as tin precursor compound. ... 

C Skeletal Nickel Catalysts - Uses Raney nickel catalysts are used in a wide range of organic synthesis reactions including ... 

Table 1. Surface properties of skeletal nickel catalysts produced by leaching a 50wt% Ni alloy in aqueous sodium hydroxide solution (compiled from refs. 16, 18 and 19).

Table 2. Industrial applications of skeletal nickel catalysts.

The addition of a second component in metal catalysts is widely used in order to enhance activity and/or selectivity. In the case of skeletal nickel catalysts it is a simple procedure to add small amounts of a second metal during the alloy preparation stage. Although other metals have been used in laboratory studies, the most common metals used to promote skeletal nickel catalysts employed industrially are Co, Cr, Cu, Fe, and Mo. 

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... 

The skeletal nickel catalyst (Ni) was prepared by leaching a 50 wt% Ni-Al alloy with 20 wt% Na0H-H20 solution at 50 °C as desrcibed elsewhere [14]. Modification of Raney Ni catalyst with... 

On a skeletal nickel catalyst and nickel catalysts alloyed with titanium and molybdenum, imder conditions where the process is controlled by activation of hydrogen, electron-acceptor substituents reduce the hydrogen concentration at the surface even more by increasing the adsorption of the nitro compound, and this in the final count leads to a decrease in the rate or complete cessation of reduction. By reducing the adsorption capacity of the nitro compound, electron-donor substituents under same conditions create a more favorable ratio of reactants at the catalyst surface and accelerate the process. 

Palladium containing alumina supported catalysts were designed for hydrodechlorination of chlorobenezne and for conversion of 4-chloro-2-nitroaniline, in which both hydrodechlorination and reduction steps are involved. Best results were obtained on catalysts containing palladium in ionic form. For reductive amination of acetone a skeletal nickel catalyst and its tin modified version was designed. On these catalysts the ratio of primary to secondary amines could be controlled and the fonuation of isopropyl alcohol was strongly suppressed. 

The phase composition of skeletal nickel catalysts was studied by using a Phillips 1700 powder diffractometer equipped with a graphite monochromator and CuK radiation. ESR spectra were recorded at 20°C using a OEOL 0ES-FE3X spectrometer. XPS measurements were taken by using a VG ESCA 3 spectrometer with an aluminium K... 

In the leaching process diluted NaOH was used. Only half of the aluminium in the alloy was leached out. In this way the high mechanical stability of the alloy could be maintained. The condition of leaching was favourable for the formation of oxygen containing surface species of aluminium. The A1 and Ni content of the catalysts was 22 and 54 w%, respectively, XRD measurements performed on the thermally treated skeletal nickel catalyst indicated the presence of metallic Ni, Al2Ni2, AlNi, NiO, AlCOHl and AlOCOHJ phases. 

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