Nickel catalysts principle

In principle biomass is a useful fuel for fuel cells many of the technologies discussed above for using biomass as a fuel produce either methane or hydrogen directly and as highlighted below synthesis gas production from biomass for conversion to methanol is an attractive option. Cellulose-based material may be converted to a mixture of hydrogen (70% hydrogen content recovered), CO2 and methane by high-temperature treatment with a nickel catalyst. 

Among the various strategies [34] used for designing enantioselective heterogeneous catalysts, the modification of metal surfaces by chiral auxiliaries (modifiers) is an attractive concept. However, only two efficient and technically relevant enantioselective processes based on this principle have been reported so far the hydrogenation of functionalized p-ketoesters and 2-alkanons with nickel catalysts modified by tartaric acid [35], and the hydrogenation of a-ketoesters on platinum using cinchona alk oids [36] as chiral modifiers (scheme 1). 

The substitution of nickel for palladium catalyst precursors has, in principle, two advantages the lower price of the metal and the lower tendency to plate. The effectiveness of nickel in the carbonylation of ethene to low molecular weight polyketones has been known for a long time [4]. Only recently, however, have nickel catalyst precursors with a reasonably high catalytic activity been discovered. The newest compounds are nickel complexes, which are modified by semicorrine-type ligands (Scheme 8.10). 

Leod gauge, and pumps. Surrounding the sample, which may be 5 to 10 g. of pelleted catalyst, there is a primary solenoid of 3100 turns carrying about 1 amp. stabilized 230 v. A.C. The secondary coil consists of 50 turns compactly surrounding the sample. This is connected in opposition to an identical coil and to a vacuum-tube voltmeter giving a maximum sensitivity of 1 mv. full scale. The principle is a very old one described by Weber over one himdred years ago. It has recently been used in a magnetic estimation of particle size in nickel catalysts as mentioned above (7). 

The simplest way to combine catalysis in a polar medium and product separation is shown in Figure 1, where both operations proceed in one unit. The nonpolar phase can be separated at the top of the column while the polar catalyst phase remains in the reactor. This principle is realized in the SHOP process using 1,4-butanediol with a nickel catalyst as the catalytic phase. 

Many late transition metals such as Pd, Pt, Ru, Rh, and Ir can be used as catalysts for steam reforming, but nickel-based catalysts are, economically, the most feasible. More reactive metals such as iron and cobalt are in principle active but they oxidize easily under process conditions. Ruthenium, rhodium and other noble metals are more active than nickel, but are less attractive due to their costs. A typical catalyst consists of relatively large Ni particles dispersed on an AI2O3 or an AlMg04 spinel. The active metal area is relatively low, of the order of only a few m g . ... 

A favorable combination of valence forces of both components seems to be the basic principle of the nickel-molybdenum ammonia catalyst. It has been found (50) that an effective catalyst of this type requires the presence of two solid phases consisting of molybdenum and nickel on the one hand and an excess of metallic molybdenum on the other. Similar conditions prevail for molybdenum-cobalt and for molybdenum-iron catalysts their effectiveness depends on an excess of free metal, molybdenum for the molybdenum-cobalt combination and iron for the molybdenum-iron combination, beyond the amounts of the two components which combine with each other. A simple explanation for the working mechanism of such catalysts is that at the boundary lines between the two phases, an activation takes place. In the case of the nickel-molybdenum catalyst, the nickel-molybdenum phase will probably act preferentially on the hydrogen and the molybdenum phase on the nitrogen. 

There has been to some degree the belief that Mossbauer spectroscopy, although in principle an ideal technique for catalyst studies, for practical purposes can only be applied to problems in catalysis if the catalyst contains either iron or tin. Therefore, one of the main purposes of this review is to show how Mossbauer spectroscopy can be directly extended to many additional Mossbauer atoms or isotopes (such as antimony, europium, nickel, ruthenium, gold, and tungsten) and, perhaps more importantly, how the technique can be extended to obtain information about systems that do not contain a Mossbauer atom. ... 

In principle pentadienyls can bond to transition elements in at least three basic ways, tj3, and tjs (Fig. 1). These can be further subdivided when geometrical factors are considered. If r 5 coordination could be converted to rj3 orr/1, one or two coordination sites could become available at the metal center, and perhaps coordinate substrate molecules in catalytic processes. Little is known about the ability of pentadienyl complexes to act as catalysts. Bis(pentadienyl)iron derivatives apparently show naked iron activity in the oligomerization of olefins (144), resembling that exhibited by naked nickel (13). The pentadienyl groups are displaced from acyclic ferrocenes by PF3 to give Fe(PF3)5 in a way reminiscent of the formation of Ni(PF3)4 from bis(allyl)nickel (144). 

Subsequent investigations revealed that, in principle, styrene undergoes isospecific polymerisation in the presence of heterogeneous Ziegler Natta catalysts [1-4], Although polystyrene of isotactic structure was also prepared with the use of homogeneous nickel-based coordination catalysts, it appeared to be of low molecular weight [22,23]. 

The reaction is conveniently carried out in a, flask flitted with a drop funnel through which the water is slowly admitted. Some hydrogen peroxide is simultaneously produced. The evolution of oxygen is facilitated by the addition of a, catalyst., such as a salt of nickel, cobalt, or copper. When pressed into small blocks or cubes, the mixture of sodium peroxide and catalyst may be placed in a Kipp or other gasgenerating apparatus based on a similar principle, and a steady supply of oxygen obtained. The commercial commodity known as oxylithc has the following composition ... 

In principle, many different reagents could add to a double bond to form more stable products that is, the reactions are energetically favorable. Not all of these reactions have convenient rates, however. For example, the reaction of ethylene with hydrogen (to give ethane) is strongly exothermic, but the rate is very slow. A mixture of ethylene and hydrogen can remain for years without appreciable reaction. Adding a catalyst such as platinum, palladium, or nickel allows the reaction to take place at a rapid rate. 

The complexes [Rh(H)(CO)(S4)] and [Ru(H)(PCy3)(S4)] differ from the nickel site in [NiFe] hydrogenases with respect to structure and metal centers, however, they evidently meet several of the principles that must hold true for enzyme centers and competitive catalysts alike. In this case, the complexes... 

In principle, the SBA/Topspe process consists in mixing the burner exit gases with steam and sending the mixture to a fixed-bed reactor on a nickel base catalyst, at about 2.10 Pa absolute and about 950 C This technique, sometimes called partial catalytic oxidatioEu is only applied to the conversion of natural gas, LPG and naphthas, particularly because, if heavier feeds are used, problems arise in the prior separation of sulfur derivatives that cannot be t[Pg.42]

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