Ni-Cu catalysts

Trickle bed reaction of diol (12) using amine solvents (41) has been found effective for producing PDCHA, and heavy hydrocarbon codistiUation may be used to enhance diamine purification from contaminant monoamines (42). Continuous flow amination of the cycloaUphatic diol in a Hquid ammonia mixed feed gives >90% yields of cycloaUphatic diamine over reduced Co /Ni/Cu catalyst on phosphoric acid-treated alumina at 220°C with to yield a system pressure of 30 MPa (4350 psi) (43). 

The authors showed that the Grabke-type kinetic model can explain the results at a low carbon activity for Ni-Cu catalysts, but that at higher carbon activities, the rates for the Ni0 9Cu0 j catalysts are higher than the model-predicted rates. Low-temperature decomposition of methane over the silica-supported Ni catalyst has been reported by Kuijpers et al. [101]. It was demonstrated that at temperatures as low as 175°C, methane adsorbed on the Ni catalysts dissociates completely into adsorbed carbon atoms and hydrogen. 

Li et al. [Ill] reported the simultaneous production of hydrogen and nanocarbon by decomposition of methane on Ni and Ni-Cu catalysts. The authors demonstrated the production of hydrogen with a purity of 80 vol% over 10 h simultaneously, 180 g of nanotubes... 

Alstrup, I. and Tavares, T., Kinetics of carbon formation from CH4-H2 on silica-supported nickel and Ni-Cu catalysts, /. Catal., 139, 513,1993. 

LIQUID-PHASE SELECTIVE HYDROGENATION OF 1,4-BUTYNEDIOL ON SUPPORTED Ni and Ni-Cu CATALYSTS. 

AIPO4 could be an adequate support component to enable a tailored Ni-Cu catalyst to obtain the most appropriate activity and selectivity in the semihydrogenation of 1,4-butynediol, not only due to its high degree of selectivity toward the olefinic compound, but also because there was no formation of other side reaction products, as described (refs. 2 and 11) in the literature. 

Of course, researchers had wondered about the surface composition before. Takeuchi et al. (7a, 7b) were the first to provide experimental evidence of the surface composition being different from the bulk composition in Ni-Cu catalysts by reaction with HC1. In a later paper (7c) they concluded that the... 

Figure 5.2.6 I Effect of alloy composition on the rates of ethane hydrogenolysis and cyclohexane dehydrogenation on Ni-Cu catalysts. (Figure from Catalytic Hydrogenolysis and Dehydrogenation Over Copper-Nickel Alloys by J. H.

Fig. 3.1 Areal turnover frequencies for ethane hydrogenolyses and cyclohexane dehydrogenations run over Ni/Cu catalysts having increasing copper content. (Redrawn using data from Ref 28).

Figure 2.9 Activities of Ni-Cu catalysts for the hydrogenolysis of ethane to methane and the dehydrogenation of cyclohexane to benzene (6). (Reprinted with permission from Academic Press, Inc.)...

Fig. 9a. Ethane hydrogenolysis and cyclohexane dehydrogenation on Ni-Cu catalysts as a function of Cu content and a 2-wt% Rh/Ti02 catalyst (H/Rh = 0.48) as a function of reduction temperature. (After Ref. 22.)...

We can conclude that Sepiolite could be an adequate support component to enable tailored Ni-Cu catalysts in oil and fat hydrogenation by taking into account how similar the results are when sepiolite is used as the support... 

Table 4.13. demonstrates the effect of various methods of preparation on the phase composition of Ni-Cu catalysts modified with tartaric acid and on their catalytic and enantioselective properties during hydrogenation of EAA (according to Zubareva et al. ). 

Figure 4.11. X-ray photoelectronic spectra of Ni3p and Cu3p (a), Ni2p (b) and Cu2p (c) of different Ni-Cu catalysts.

The data on differential thermal desorption spectra of the reduction of NiO and CuO proved to be very important. Despite the differences in reduction temperatures of individual oxides (320°C and 270°C), a maximum ee was observed at that reduction when mixture of oxides were reduced at a lower temperature, 220°C, because Ni-Cu catalysts contain two phases a Cu phase and a Cu-Ni-alloy phase. With increase of the copper content, the Ni-Cu phase is enriched in the bulk with Ni and on the surface with Cu. According to Klabunovskii et al. the Ni-Cu (70 30) catalyst is five times more active than the pure Cu catalyst, but after modification of this catalyst with TA, its enantioselectivity in the hydrogenation of EAA was lower than either the modified pure Cu catalyst ee 50%) or pure Ni-TA catalyst ee 33%) under the same conditions. Thus the bimetallic Ni-Cu catalysts revealed S5mergism in catalytic activity but not in enantioselectivity. 

Increasing the copper content of the mixed Ni-Cu, inactivates the catalysts, because copper, as an inactive component and dilutes the Ni centers responsible for enantioselectivity. The specific activity related only to the Ni-Cu alloy phase in the concentration range of 20-80 mol% Cu (Figure 4.12.), so the ee and the specific rate remained constant corresponding to the constancy of the surface concentration of the active component in the Ni-Cu catalysts. 

Figure 4.12. Effect of the composition of Ni-Cu catalysts, modified with TA, on the reaction rate (left) and on the ee (right) in the hydrogenation of EAA...

Increasing the fraction of Ni in the Ni-Cu catalysts leads to segregation of Ni on the surface, which was confirmed by Chernysheva et al. in the hydrogenation of EAA on Ni-Cu catalysts modified with (S)-phenylalanine, S -Phe. Indeed, on the Cu-S -Phe catalyst the product (S)-(+)-EHB was obtained, whereas on the Cu-Ni catalyst, (90 10) modified with S -Phe, another enantiomer, the (7 )-(-)-EHB, was obtained. The latter product was also observed on Ni-S-Phe. This fact confirmed that Ni was segregated on the surface of the Ni-Cu catalysts with the maximum Ni contents of 20-40% (see Figure 4.13.)... 

It was found that tartaric acid as a modifier forms complexes on the surface of Ni-silica and Cu-silica catalysts in which IR spectra reveal quite close coordination between the COOH groups. This is confirmed by similar values of ee in which Ni-silica catalysts are modified at pH 5 and pH 10. The similarity of the effect of pH of the modifying solution on Ni and Ni-Cu catalysts indicate that the structure of chiral clusters on the surface of both catalysts remained unchanged. Probably additional introduction of copper into Ni-Cu catalyst did not produce any ligand effect and did not change the behaviour of chiral clusters, but only changed the number of such clusters ( cluster effect ). 

The dependences of ee and rate of hydrogenation of EAA on the composition of Ni-Cu catalysts indicate that the centers of enantioselective hydrogenation contain four times more chiral species (atoms and clusters) than centers of "racemic" hydrogenation leading to racemic EHB. 

Supported chiral Ni and Ni-Cu catalysts i 9-i60-24s,248,249 special interest because they allow the elucidation of the nature of the metal-support interaction and the asymmetric adsorption of modifier and substrate molecules by use of the IR spectra of adsorbed molecules. 

In the case of Ni-Cu-aerosil catalysts ee s and reaction rates underwent sharp decreases upon adding small amounts of copper into a Ni catalyst. Infrared spectra of supported 20% (Ni-Cu)-TA catalysts of different Ni-Cu compositions showed the interaction of the Ni-Cu phase with both COOH groups of tartaric acid but in different states depending on the ratios of Ni Cu. A lower covalent character of binding of the TA with metals was observed for Ni-Cu catalysts of composition 1 1. ... 

Hydrogenation of fats and fatty acids in a tank reactor with a turbine stirrer (110-120 rpm) H2 is introduced through a distributor at the bottom, 150-200 °C, up to 30 bar, Ni/Cu catalysts. 

The whisker growth mechanism is also blocked by sulphur poisoning of the nickel surface. When formed, the carbon has a typical octopus structure with several fibres growing fi-om one nickel crystal [390], As shown in Figure 5.8, a similar stmctuie is formed on Ni/Cu catalysts with high copper contents [49],... 

Choi and Park [7] reported that there is a large increase in the yield of TFE (76-90%) at 700°C when using copper instead of Inconel as reactor tube material. A recent Mandarin language paper, which could not be obtained, also reported greatly increased yields of TFE when R-22 (CHCIF) was pyrolyzed over a 60/40% Ni—Cu catalyst, supporting the findings of Choi and Park. 

In addition, oxazole-4-carboxylate 10 can be subjected to direct Pd-catalyzed alkenylation, benzylation, and alkylation in the 2-position [257]. Recently, direct 2-C-H-functionaUzation (alkylation and arylation) has been reported for oxazoles (as well as thiazoles and benzazoles) with free 2-position utihzing chelated Ni/Cu-catalysts derived from 2,2 -bis(dimethylamino)diphenylamine [258] or chelated Cu/Pd-complexes derived from Xantphos ]259] in the presence of a base. 

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