Nickel-copper alloy catalysts

Dowden and Reynolds (49,50) in further experimental work on the hydrogenation of benzene and styrene with nickel-copper alloys as catalysts, found a similar dependence. The specific activities of the nickel-copper alloy catalysts decreased with increasing copper content to a negligible value at 60% copper and 30-40% copper for benzene and styrene, respectively. Low-temperature specific heat data indicated a sharp fall (1) in the energy density of electron levels N(E) at the Fermi surface, where the d-band of nickel becomes filled at 60 % copper, and (2) from nickel to the binary alloy 80 nickel -)- 20 iron. Further work by these authors (50) on styrene hydrogenation with nickel-iron alloy... 

Figure 2.8 Isotherms for total hydrogen adsorption (circles) and weakly adsorbed hydrogen (squares) at room temperature on unsupported nickel and copper catalysts and on a nickel-copper alloy catalyst (6). (Reprinted with permission from Academic Press, Inc.)...

Alstrup I, Tavares M T, Bernardo C A, Sprensen O, Rostrup-Nielsen J R, Carbon formation on nickel and nickel-copper alloy catalysts , Materiais and Corrosion,... 

This conclusion was additionally confirmed by Palczewska and Janko (67) in separate experiments, where under the same conditions nickel-copper alloy films rich in nickel (and nickel films as well) were transformed into their respective hydride phases, which were proved by X-ray diffraction. The additional argument in favor of the transformation of the metal film into hydride in the side-arm of the Smith-Linnett apparatus consists of the observed increase of the roughness factor ( 70%) of the film and the decrease of its crystallite size ( 30%) after coming back from low to high temperatures for desorbing hydrogen. The effect is quite similar to that observed by Scholten and Konvalinka (9) for their palladium catalyst samples undergoing the (a — j8) -phase transformation. 

Nickel compounds as catalysts, 191 Nickel-copper alloys, 252, 253 atomic hydrogen recombination, 273-279... 

This review is followed by a consideration of some of the features characteristic of hydrocarbon reactions on catalysts comprising individual metals from Groups VIII and IB of the periodic table. Finally, the activities of a series of unsupported nickel-copper alloys for hydrogenolysis and dehydrogenation reactions are discussed. These latter studies were made to obtain information on the selectivity phenomenon with bimetallic catalysts of known structure. The nickel-copper alloys were characterized by a variety of chemical and physical probes. 

The work with nickel-copper alloys led to a better understanding of the selectivity phenomenon than did the original exploratory studies on supported bimetallic catalysts, since the supported catalysts were difficult to characterize with techniques available at that time. Nevertheless, the early exploratory studies were important in disclosing the selectivity phenomenon and in providing incentive to conduct further research. 

Nickel-copper alloys provide a good example of a bimetallic catalyst system in which the variation of catalytic activity with composition depends markedly on the type of reaction, thus leading to substantial selectivity effects. The catalysts to be considered here are alloy powders with a surface area of approximately 1 m2/g (6). Approximately one atom out of a thousand is a surface atom in such catalysts. 

Each alloy catalyst was prepared by a coprecipitation method in which ammonium bicarbonate was added to an aqueous solution of nickel and copper nitrates. The resulting precipitate was dried and heated in air at 370°C to form a mixture of nickel and copper oxides. The mixed oxides were then reduced in hydrogen in several stages over a range of temperatures to produce the nickel-copper alloy. The reduction was completed at 400°C. 

Binary nickel-copper alloys have already been investigated as substitutes for nickel catalysts in order to reduce the amount of coking because of the noncatalytic nature of copper [15-18], Nickel-copper alloys, however, have never been tested for their resistance to metal dusting. The aim of this work was to study the effects of adding copper on the behaviour of nickel metal dusting and associated coking. 

Recently, other authors when studying the activation of hydrogen by nickel and nickel-copper catalysts in the hydrogen-deuterium exchange reaction concentrated for example only on the role of nickel in these alloys (56) or on a correlation between the true nickel concentration in the surface layer of an alloy, as stated by the Auger electron spectroscopy, and the catalytic activity (57). 

The temperature behavior of the alloy catalysts in the heterogeneous recombination of hydrogen atoms was different for rich in nickel alloys from one side and for rich in copper from the other. For the three alloy catalyst films, i.e. Ni97Cu3, Ni77Cu23, and Ni57Cu43 (numbers represent... 

Fig. 6. Activities of copper-nickel alloy catalysts for the hydrogenolysis of ethane to methane and the dehydrogenation of cyclohexane to benzene. The activities refer to reaction rates at 316° C. Ethane hydrogenolysis activities were obtained at ethane and hydrogen pressures of 0.030 and 0.20 atm., respectively. Cyclohexane dehydrogenation activities were obtained at cyclohexane and hydrogen pressures of 0.17 and 0.83 atm, respectively (74).

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