Nickel-activated carbon catalysts preparation

Another specific feature of the catalytic behavior of the structures under study consists in that the chemical nature of a metal becomes a factor less important for catalysis as the surface nanoparticles density increases. This is well seen in Figure 15.14, which shows the results obtained in measurements of the activity of copper- and nickel-based catalysts in the reaction of carbon tetrachloride addition to olefins. Presented in this figure are the activities of catalysts prepared by laser electrodispersion and the conventional deposition techniques. Two important features are worth noting. First, the activity... 

Nickel, cobalt, copper catalysts supported on oxides or activated carbon are prepared following this procedure and are used for the liquid phase hydrogenation of long chain nitriles. Their activities and selec-tlvities towards the formation of amines (primary, secondary, tertiary) are compared with the one obtained with conventional catalysts. 

Various carbon-based catalysts were tested in the investigated air gas-diffusion electrodes pure active carbon [6], active carbon promoted with silver [7] or with both silver and nickel. Catalysts prepared by pyrolysis of active carbon impregnated with a solution of the compound Co-tetramethoxyphenylporphyrine (CoTMPP) are also studied [8],... 

The feasibility of carbon-supported nickel-based catalysts as the alternative to the platinum catalyst is studied in this chapter. Carbon-supported nickel (Ni/C, 10 wt-metal% [12]), ruthenium (Ru/C, 10 wt-metal% [12]), and nickel-ruthenium composite (Ni-Ru/C, 10 wt-metal%, mixed molar ratio of Ni/Ru 0.25,1,4, 8, and 16 [12]) catalysts were prepared similarly by the impregnation method. Granular powders of the activated carbon without the base pretreatment were stirred with the NiCl2, RuC13, and NiCl2-RuCl3 aqueous solutions at room temperature for 24 h, respectively. Reduction and washing were carried out in the same way as done for the Pt/C catalyst. Finally, these nickel-based catalysts were evacuated at 70°C for 10 h. 

The phase-transfer catalysed reaction of nickel tetracarbonyl with sodium hydroxide under carbon monoxide produces the nickel carbonyl dianions, Ni,(CO) 2- and Ni6(CO)162, which convert allyl chloride into a mixture of but-3-enoic and but-2-enoic acids [18]. However, in view of the high toxicity of the volatile nickel tetracarbonyl, the use of the nickel cyanide as a precursor for the carbonyl complexes is preferred. Pretreatment of the cyanide with carbon monoxide under basic conditions is thought to produce the tricarbonylnickel cyanide anion [19], as the active metal catalyst. Reaction with allyl halides, in a manner analogous to that outlined for the preparation of the arylacetic acids, produces the butenoic acids (Table 8.7). 

A large number of intermediate pathways arc possible when catalytic reactions interfere with the polymerization-dehydrogenation steps. A common scenario is the catalytic dehydrogenation of hydrocarbons on nickel surfaces followed by dissolution of the activated carbon atoms and exsolution of graphene layers after exceeding the solubility limit of carbon in nickel. Such processes have been observed experimentally [40] and used to explain the shapes of carbon filaments. In the most recent synthetic routes to nanotubes [41] the catalytic action of in situ-prepared iron metal particles was applied to create a catalyst for the dehydrogenation of cither ethylene or benzene. 

L. M. S. Silva, J. J. M. Orfao and J. L. Figueiredo. Formation of two metal phases in the preparation of activated carbon-supported nickel catalysts. Applied Catalysis A General, 209, 145-154 (2001). 

The nickel catalyst (about 50 wt% nickel on kieselguhr) was prepared by an ordinary precipitation method. Sodium carbonate solution was added to a slurry of kieselguhr and nickel nitrate solution at 70 °C and precipitate was obtained. This precipitate was washed with water thoroughly and then was dried at 105 C for 12 hrs, crushed to 60-150 mesh, calcined at 350 C for 4 hrs. This was activated with 100% hydrogen at 200, 300 and 350 "C for 4 hrs. These prepared catalysts were stored in nitrogen atmospheric bottle and desiccator. 

A Ni-As(B) catalyst prepared by the borohydride reduction of alumina-supported nickel arsenate gave, on hydrogenation of 1-bromo-l 1-hexadecyne (13) in the presence of a small amount of acetone, a 97% yield of the alkene (14) having a 92 5 cis/trans ratio. No hydrogenolysis of the carbon-bromine bond occurred. "> 2 Borohydride reduction of cobalt acetate gave a Co(B) catalyst that was somewhat less active than Ni(B) but that was quite selective in alkyne semihydrogenations (Eqn. 16.20). ... 

The conversion of carbon dioxide on the catalysts prepared from nickel-rich amorphous Ni-Zr alloys is improved by the addition of samarium. On the other hand, the activity of the zirconium-rich catalysts is not influenced by the addition of samarium. The predominant formation of tetragonal zirconia in the nickel-rich Ni-Zr-Sm catalysts, in contrast to the formation of two types (monoclinic and tetragonal) of zirconia in the zirconium-rich Ni-Zr-Sm catalysts, appears to be responsible for the higher catalytic activity of the nickel-rich catalysts in addition to their higher surface area than the corresponding samarium-free Ni-Zr catalysts. 

The experiments were conducted in a fixed bed flow type reactor under pressurized conditions as have been reported in detail elsewhere (ref. 2). Methanol (MeOH) and methyl iodide (Mel) were mixed and fed with a high-pressure microfeeder. Catalysts were prepared by impregnating a commercially available granular active carbon (A.C., Takeda Shirasagi C, 20-40 mesh) with nickel acetate and drying at 120 °C for 12 h in an air oven. They were used without any further pretreatment. 

A most satisfactory comparison of the activities of supported and unsupported catalysts of silver, copper, and nickel may be obtained from the results of experiments made by Faith and Keyes,803 who worked with methanol and ethanol. The fact that uniform methods of catalyst preparation, support, and size, and uniform methods of operations were used adds much to the value of the results. In all cases the catalyst mass was 45 mm. long by 12 mm. in diameter, the alcohol saturator was maintained at 45° C. for ethanol and at 36° C. for methanol, and the temperature of the hottest point in the catalyst mass was determined with a thermocouple embedded in the mass. In the case of ethanol oxidation the highest conversions to acetaldehyde per pass were obtained under the following conditions (1) silver gauze catalyst flow rate 0.57 liters per minute catalyst temperature 515° C., 80.6 per cent conversion to aldehyde 13.3 per cent conversion to carbon dioxide and 3.2 per cent conversion to add, (2) silver oxide supported on asbestos flow rate 0.37 liters per minute catalyst temperature 595° C. (conversions as above) 72.3 per cent 14.5 per cent 2.9 per cent, (3) copper turnings catalyst flow rate 0.62 liters per minute catalyst temperature 512° C. (conversions) 78.0... 

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