Activated carbon/transition metal catalysts

Abstract—Carbon nanotubules were produced in a large amount by catalytic decomposition of acetylene in the presence of various supported transition metal catalysts. The influence of different parameters such as the nature of the support, the size of active metal particles and the reaction conditions on the formation of nanotubules was studied. The process was optimized towards the production of nanotubules having the same diameters as the fullerene tubules obtained from the arc-discharge method. The separation of tubules from the substrate, their purification and opening were also investigated. 

Mikami M, Hatano M, Akiyama K (2005) Active Pd(II) Complexes as Either Lewis Acid Catalysts or Transition Metal Catalysts. 14 279-322 Minatti A, DOtz KH (2004) Chromium-Templated Benzannulation Reactions. 13 123-156 Miura M, Satoh T (2005) Catalytic Processes Involving b-Carbon Elimination. 14 1-20 Miura M, Satoh T (2005) Arylation Reactions via C-H Bond Cleavage. 14 55-84 Mizobe Y, see Hidai M (1999) 3 227-241... 

Not all C-H activation chemistry is mediated by transition metal catalysts. Many of the research groups involved in transition metal catalysis for C-H activation have opted for alternative means of catalysis. The activation of methane and ethane in water by the hexaoxo-/i-peroxodisulfate(2—) ion (S2O82) was studied and proceeds by hydrogen abstraction via an oxo radical. Methane gave rise to acetic acid in the absence of external carbon monoxide, suggesting a reaction of a methyl radical with CO formed in situ. Moreover, the addition of (external) CO to the reaction mixture led to an increase in yield of the acid product (Equation (ll)).20... 

Not only heteroatom-H bonds but also activated C-H bonds can add to the jr-system of an allene. Since carbon lacks a free electron pair, the transition metal catalyst must first activate the C-H bond the new species formed will then react with the C=C double bond. For efficient activation of that kind, two acceptors (typically esters, nitriles and/or sulfones) are necessary. In accord with this mechanistic picture is the fact that the reaction does not benefit from an additional base (which would deproto-nate the pronucleophile). Hence neutral conditions are even better. 

Alloying the nickel of the anode to improve tolerance for fuel contaminants has been explored. Gold and copper alloying decreases the catalytic activity for carbon deposition, while dispersing the anode with a heavy transition metal catalyst like tungsten improves sulfur resistance. Furthermore, ceria cermets seem to have a higher sulfur tolerance than Ni-YSZ cermets [75],... 

Despite the fact that carbon dioxide (C02) is used in a great number of industrial applications, it remains a molecule of low reactivity, and methods have still to be identified for its activation. Both thermodynamic and kinetic problems are connected with the reactivity of C02, and few reactions are thermodynamically feasible. A very promising approach to activation is offered by its coordination to transition metal complexes, as both stoichiometric reactions of C-C bond formation and catalytic reactions of C02 are promoted by transition metal systems. Efforts to enhance the yield of hydrogen in water gas-shift (WGS) reactions have also been centered on C02 interactions with transition metal catalysts. The coordination on metal centers lowers the activation energy required in further reactions with suitable reactants involving C02, making it possible to convert this inert molecule into useful products. 

Among common carbon-carbon bond formation reactions involving carbanionic species, the nucleophilic substitution of alkyl halides with active methylene compounds in the presence of a base, e. g., malonic and acetoacetic ester syntheses, is one of the most well documented important methods in organic synthesis. Ketone enolates and protected ones such as vinyl silyl ethers are also versatile nucleophiles for the reaction with various electrophiles including alkyl halides. On the other hand, for the reaction of aryl halides with such nucleophiles to proceed, photostimulation or addition of transition metal catalysts or promoters is usually required, unless the halides are activated by strong electron-withdrawing substituents [7]. Of the metal species, palladium has proved to be especially useful, while copper may also be used in some reactions [81. Thus, aryl halides can react with a variety of substrates having acidic C-H bonds under palladium catalysis. 

The C-H bond cleavage of active methylene compounds with a transition metal catalyst is another method for the functionalization of these C-H bonds. To date, several reactions have been developed. In particular, the asymmetric version of this type of catalytic reaction provides a new route to the enantioselective construction of quaternary carbon centers. One of the most attractive research subjects is the catalytic addition of active methylene C-H bonds to acetylenes, allenes, conjugate ene-ynes, and nitrile C-N triple bonds. The mthenium-catalyzed reaction active methylene compounds with carbonyl compounds involving aldehyde, ketones, and a,y3-unsatu-rated ketones and esters is described in this section. 

Except for the metallic impurities present on the walls of poorly washed glassware, no other transition metal catalyst may be assumed to be present in this experiment. Consequently, the transfer of the dimethylamino group from the ortho amide II to I must be taking place under less energy demanding conditions, where protic acid catalysis suffices to activate the triple carbon to carbon bond. ... 

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