Nickel catalysts comparison

In comparison to the Ziegler catalyst, the use of the nickel catalyst system offers the following advantages [34] ... 

The comparison of several nickel catalyst for the arylation of alcohols with arylbromide has been performed, in the same conditions of time, temperature and base, using different oxygen, phosphorus and nitrogen ligands. The yields for each catalyst, shown in the table (Fig. 9) range from 5 to 80 %. 

These results point out, for the arylation of alcohols, a better activity of the nickel catalysts in comparison to the copper analogs. That might be probably connected to the harder character of nickel(II) complexes in comparison to the copper analogs. 

A new comparison of the copper and nickel catalysts (Fig. 12) on the arylation of alcohols, using potassium carbonate as base, shows once again the superiority of the nickel catalyst (70 % against 40 % for the copper catalyst). 

The Nickel catalyst used for comparison was Calsicat E472D from Mallinckrodt Specialty Chemicals containing 22% Ni. 

Fig. 2. (a) A comparison of the rate of methane synthesis over single crystal nickel catalysts and supported Ni/AliO, catalysts at 120 torr total reactant pressure. (From Rtf. 12.) (b) Atomic configuration of a Ni(100) surface, (c) Atomic configuration of a... 

The single crystal results are compared in Fig. 2 with three sets of data taken from Ref. 13 for nickel supported on alumina, a high surface area catalyst. This comparison shows extraordinary similarities in kinetic data taken under nearly identical conditions. Thus, for the Hj-CO reaction over nickel, there is no significant variation in the specific reaction rates or the activation energy as the catalyst changes from small metal particles to bulk single crystals. These data provide convincing evidence that the methanation reaction rate is indeed structure insensitive on nickel catalysts. 

The structure effects on the hydrogenation rate of ketones also have been used for comparisons of catalysts. Simonikova, Ralkova, and Kochloefl 113) have pointed out that the slopes of the Taft relationships for series 91-93 for copper, platinum, and rhodium catalysts, together with the similar results of Iwamoto, Yoshida, and Anouma 112) for a nickel catalyst (series 90), exhibit an opposite trend from the d character of the metals. 

The only difference between the two samples is the gold modification of the nickel nanoclusters. In these investigations, n-butane was used to test the activity, because it is known to cause the most severe graphite formation problems. Whereas the pure nickel catalyst was deactivated rapidly as a result of the formation of graphite, as confirmed by electron microscopy, for example, it was found that the conversion catalyzed by the gold/nickel sample was maintained almost constant. This comparison is consistent with the inference that the novel gold/nickel catalyst did not... 

FlG. 25. Comparison of the deterioration with time of Raney-nickel catalyst under different operation conditions. (Jenseit, W., Khalil, A., Wendt, H., 2. Appl. Electrochem. 20,893(1990)). 

The introduction by Raney (1927) of a new form of catalyst (the Raney nickel catalyst) with enhanced activity for hydrogenation at low pressures and temperatures in comparison with the usual form of nickel catalyst as employed by Sabatier and Senderens opened up a new field of controlled catalytic hydrogenation. A special alloy, prepared essentially by the fusion of approximately equal parts of aluminium and nickel at 1200-1500 °C, is treated with alkali which dissolves the aluminium and leaves the nickel as a finely-divided black suspension. The catalyst is thoroughly washed to free it from alkali, is stored under absolute ethanol in an air-free container and is measured in the... 

The amount of wash coat which was deposited in the testing reactors was in the same range, between 14 and 17 mg, for the rhodium, platinum and palladium samples tested. The platinum sample was calcined after impregnation at a lower temperature of 450 °C, all other samples at 800 °C. The reason for this will be explained below. The content of the active noble metal was around 5 wt.%. All noble metal-containing samples were laboratory-made catalysts. A commercial a-alumina-based catalyst containing 14 wt.% Ni was added for comparison, as nickel catalysts are applied in industrial steam reforming [52],... 

A model manure solution was prepared based on 10% glucose (as a carbohydrate hydrolysate model) with the various mineral components. The model solution was processed with three different catalyst formulations for comparison. The two nickel catalysts, ruthenium stabilized and copper stabilized (4), exhibited no effects from the contaminants, while the ruthenium showed reduced activity similar to that already noted. 

Comparison of Methanation Activities for Zeolite and Alumina Supported Nickel Catalysts... 

Fig. 17 shows a comparison of the time-on-stream behavior of the three nickel catalysts. The data include the conversion of propane and corresponding mass changes. It is evident that the initiation of carbon formation proceeds especially easily on the PR-S catalyst under these conditions. In contrast, no carbon was observed on PR-F under similar conditions during a 30-h period. The gas composition in the experiment with SR-F (Fig. 17) was different with a considerably lower carbon-production potential. Still, the carbon formation was initiated readily,... 

Temperature control was demonstrated in a series of experimental tests [8-10]. In one series of tests, both ceramic and metal honeycomb monolith supports were used [8,9]. The ceramic supports used in these tests were 46.5-cells/cm (square cells) Celcor monoliths 6.2 cm in diameter and 10.2 cm long, whereas the metal honeycomb monolith supports (made of Kanthal, a high-temperature alloy) had 38.8 cells/cm (hexagonal cells) and were 6.3 cm in diameter and 5.1 cm long. The ceramic and metal monoliths were washcoated with gamma alumina, and the nickel catalyst loadings were 13 and 5.6% (average), respectively. In comparison, the conventional catalyst used for reference was... 

Comparative tests have been performed in the semi-batch reactor system to evaluate the Ru/Ti02 cataly versus a more conventional nickel-based catalyst. These tests show that rutlienium at only 3% metal loading has about the same activity as nickel at S0% metal loading. This comparison is only for short-term activity of the catalyst. As demonstrated in the continuous flow tests, the nickel catalyst loses activity readily in tlie first hours on stream, while the ruthenium maintains its activity. 

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