Nickel catalytic activity

The polyethylenes obtained present a typical bimodal molecular weight distribution indicating the formation of non-uniform nickel catalytic active centers in the IL phase. In opposition, the polyethylenes obtained under homogeneous conditions present only a slightly bimodal molecular weight distribution. ... 

The catalytic hydrogenation of ethylene occurs on various metal catalysts, such as nickel, including active or skeletal forms produced by dissolving out... 

In the previous section efficient catalysis of the Diels-Alder reaction by copper(II)nitrate was encountered. Likewise, other bivalent metal ions that share the same row in the periodic system show catalytic activity. The effects of cobalt(II)nitrate, nickel(II)nitrate, copper(II)nitrate and zinc(ll)nitrate... 

Even ia 1960 a catalytic route was considered the answer to the pollution problem and the by-product sulfate, but nearly ten years elapsed before a process was developed that could be used commercially. Some of the eadier attempts iacluded hydrolysis of acrylonitrile on a sulfonic acid ion-exchange resia (69). Manganese dioxide showed some catalytic activity (70), and copper ions present ia two different valence states were described as catalyticaHy active (71), but copper metal by itself was not active. A variety of catalysts, such as Umshibara or I Jllmann copper and nickel, were used for the hydrolysis of aromatic nitriles, but aUphatic nitriles did not react usiag these catalysts (72). Beginning ia 1971 a series of patents were issued to The Dow Chemical Company (73) describiag the use of copper metal catalysis. Full-scale production was achieved the same year. A solution of acrylonitrile ia water was passed over a fixed bed of copper catalyst at 85°C, which produced a solution of acrylamide ia water with very high conversions and selectivities to acrylamide. 

An effect which is frequently encountered in oxide catalysts is that of promoters on the activity. An example of this is the small addition of lidrium oxide, Li20 which promotes, or increases, the catalytic activity of dre alkaline earth oxide BaO. Although little is known about the exact role of lithium on the surface structure of BaO, it would seem plausible that this effect is due to the introduction of more oxygen vacancies on the surface. This effect is well known in the chemistry of solid oxides. For example, the addition of lithium oxide to nickel oxide, in which a solid solution is formed, causes an increase in the concentration of dre major point defect which is the Ni + ion. Since the valency of dre cation in dre alkaline earth oxides can only take the value two the incorporation of lithium oxide in solid solution can only lead to oxygen vacaircy formation. Schematic equations for the two processes are... 

To give an idea of the wide rai e of catalytic systems that have been investigated where chemisorption data were essential to interpret the results, some of the author s papers will be discussed. Measurements were reported on the surface areas of a very wide range of metals that catalyze the hydrogenation of ethane. In the earliest paper, on nickel, the specific catalytic activity of a supported metal was accurately measured for the first time it was shown also that the reaction rate was direcdy proportional to the nickel surface area. Studies on the same reaction... 

The nickel and cohalt aqua complexes were even more effective, both for catalytic activity and enantioselectivity, than the corresponding anhydrous complexes (Scheme 7.5). Addition of three equivalents of water to the anhydrous nickel complex recovered the catalytic efficiency. DBFOX/Ph complexes derived from manga-nese(II), iron(II), copper(II), and zinc(II) perchlorates, both anhydrous and vef. 

Among the J ,J -DBFOX/Ph-transition(II) metal complex catalysts examined in nitrone cydoadditions, the anhydrous J ,J -DBFOX/Ph complex catalyst prepared from Ni(C104)2 or Fe(C104)2 provided equally excellent results. For example, in the presence of 10 mol% of the anhydrous nickel(II) complex catalyst R,R-DBFOX/Ph-Ni(C104)2, which was prepared in-situ from J ,J -DBFOX/Ph ligand, NiBr2, and 2 equimolar amounts of AgC104 in dichloromethane, the reaction of 3-crotonoyl-2-oxazolidinone with N-benzylidenemethylamine N-oxide at room temperature produced the 3,4-trans-isoxazolidine (63% yield) in near perfect endo selectivity (endo/exo=99 l) and enantioselectivity in favor for the 3S,4J ,5S enantiomer (>99% ee for the endo isomer. Scheme 7.21). The copper(II) perchlorate complex showed no catalytic activity, however, whereas the ytterbium(III) triflate complex led to the formation of racemic cycloadducts. 

We employed malononitrile and l-crotonoyl-3,5-dimethylpyrazole as donor and acceptor molecules, respectively. We have found that this reaction at room temperature in chloroform can be effectively catalyzed by the J ,J -DBFOX/Ph-nick-el(II) and -zinc(II) complexes in the absence of Lewis bases leading to l-(4,4-dicya-no-3-methylbutanoyl)-3,5-dimethylpyrazole in a good chemical yield and enantio-selectivity (Scheme 7.47). However, copper(II), iron(II), and titanium complexes were not effective at all, either the catalytic activity or the enantioselectivity being not sufficient. With the J ,J -DBFOX/Ph-nickel(II) aqua complex in hand as the most reactive catalyst, we then investigated the double activation method by using this catalyst. 

Contaminant coke is produced by catalytic activity of metals such as nickel, vanadium, and by deactivation of the catalyst caused by organic nitrogen. 

In addition to actual synthesis tests, fresh and used catalysts were investigated extensively in order to determine the effect of steam on catalyst activity and catalyst stability. This was done by measurement of surface areas. Whereas the Brunauer-Emmett-Teller (BET) area (4) is a measure of the total surface area, the volume of chemisorbed hydrogen is a measure only of the exposed metallic nickel area and therefore should be a truer measure of the catalytically active area. The H2 chemisorption measurement data are summarized in Table III. For fresh reduced catalyst, activity was equivalent to 11.2 ml/g. When this reduced catalyst was treated with a mixture of hydrogen and steam, it lost 27% of its activity. This activity loss is definitely caused by steam since a... 

There is little data available to quantify these factors. The loss of catalyst surface area with high temperatures is well-known (136). One hundred hours of dry heat at 900°C are usually sufficient to reduce alumina surface area from 120 to 40 m2/g. Platinum crystallites can grow from 30 A to 600 A in diameter, and metal surface area declines from 20 m2/g to 1 m2/g. Crystal growth and microstructure changes are thermodynamically favored (137). Alumina can react with copper oxide and nickel oxide to form aluminates, with great loss of surface area and catalytic activity. The loss of metals by carbonyl formation and the loss of ruthenium by oxide formation have been mentioned before. 

The last vertical column of the eighth group of the Periodic Table of the Elements comprises the three metals nickel, palladium, and platinum, which are the catalysts most often used in various reactions of hydrogen, e.g. hydrogenation, hydrogenolysis, and hydroisomerization. The considerations which are of particular relevance to the catalytic activity of these metals are their surface interactions with hydrogen, the various states of its adatoms, and admolecules, eventually further influenced by the coadsorbed other reactant species. 

A short survey of information on formation, structure, and some properties of palladium and nickel hydrides (including the alloys with group IB metals) is necessary before proceeding to the discussion of the catalytic behavior of these hydrides in various reactions of hydrogen on their surface. Knowledge of these metal-hydrogen systems is certainly helpful in the appreciation, whether the effective catalyst studied is a hydride rather than a metal, and in consequence is to be treated in a different way in a discussion of its catalytic activity. 

The screened proton model of nickel or palladium hydrides and Switendick s concept of the electronic structure do not constitute a single approach sufficient to explain the observed facts. In this review, however, such a model will be used as the basis for further discussions. It allows for the explanation and general interpretation of the observed change of catalytic activity of the metals, when transformed into their respective hydrides. 

IV. The Effect of Transformation into Hydride on the Catalytic Activity of Nickel and Its Alloys with Copper... 

Experimental evidence illustrating the effect that hydrides of nickel or its alloys with copper have on the catalytic activity of the respective metals is to be found in papers which discuss catalytic consequences of the special pretreatment of these metal catalysts with hydrogen during their preparation. One must also look very carefully into cases where self-poisoning has been reported as appearing in reactions of hydrogen with other reactants. 

In order that the possibility of contamination of catalysts with traces of oxides could be eliminated Campbell and Emmett (51) studied the catalytic activity of metallic films of nickel and its alloys with copper or gold. They were deposited under a high vacuum and then sintered (alloys also homogenized) in hydrogen at 5 cm Hg pressure at 350°C or 500°C. The films were subsequently allowed to cool to room temperature and only... 

Volter and Alsdorf (52) obtained a relation of a very similar character for the dependence of the catalytic activity in formic acid decomposition on the composition of the nickel-copper alloys. However, extending the times of the alloy annealing for their better homogenization caused the maxima on the catalytic activity curves to disappear. 

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). 

On the basis of information on the properties of the nickel-hydrogen and nickel-copper-hydrogen systems available in 1966 studies on the catalytic activity of nickel hydride as compared with nickel itself were undertaken. As test reactions the heterogeneous recombination of atomic hydrogen, the para-ortho conversion of hydrogen, and the hydrogenation of ethylene were chosen. 

In these particular experiments it proved impossible to investigate the effect of copper concentration on the catalytic activity of alloys free of the hydride phase. Figure 10 69, 64a, 65) illustrates the changing values of the recombination coefficient on nickel-copper alloys related to the composition of the alloy at room temperature. The small amount of copper introduced into the nickel already distinctly decreased the catalytic ac-... 

The range of observations concerning the direct comparison of the catalytic activity of nickel and rich in nickel alloys with their respective hydride phases has been further extended on reactions of a more complicated nature such as para-ortho hydrogen conversion and ethylene hydrogenation. 

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