Surface carbonaceous intermediates produced from methane are shown to produce small alkanes upon hydrogenation below 400 K.Current practice to convert natural gas to higher hydrocarbons proceeds by the indirect route in which natural gas is first converted to synthesis gas at a high temperature.1 Subsequently, hydrocarbons are produced in a low temperature exothermic process from synthesis gas.2.3 Direct methane conversion, like pyrolysis to acetylene and benzene, can only operate at temperatures above 1200 K. 475 Oxidative coupling of methane to ethylene has been proposed as a promising alternative route6-11 and proceeds at temperatures between 850 and 1200 K.

Well reduced silica-supported rhodium catalysts contain oxygen species that are able to participate in reactions. Adsorbed CO molecules were demonstrated to exchange their oxygen atoms with oxygen atoms from these catalysts. The amount of such reactive oxygen is increased by a vanadium promoter. Using infrared adsorption, the scrambling of 13clSo to 13C160 was studied as a function of the temperature. The vanadium promoter decreases the temperature for CO scrambling. Linear adsorbed CO is the preferred initial state for this process.

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it possible to take a set of generic skeletal force constants and use these for deriving structures with acceptable accuracy. As we have shown, the skeletal force constants are not generally transferable. If, however, one only wishes to obtain good structures of linear metallocenes, these force constants can be obtained for the metals in Table VI11 by simply using those of ferrocene as a generic set, provided the correct equilibrium bond lengths and angles are used. This will probably apply even for somewhat strained linear metallocenes.Acknowledgment. This work was supported by grants from the National Institutes of Health. Homologation of Olefins with Methane on Transition MetalsTijs Koerts,+ Piet A. Leclercq Abstract: Alkylation of olefins using methane has been realized on transition metal catalysts. The main problem is to get methane dissociatively adsorbed together with an olefin. This is due to the difficult activation of the strong tetrahedral C-H bonds of methane. To react methane with an olefin, a reaction sequence is used consisting of three steps. First methane is dissociatively adsorbed between 600 and 800 K on a reduced transition metal catalyst. After cooling, an olefin is coadsorbed at a temperature between 300 and 400 K. Upon subsequent hydrogenation carbon-carbon bond formation occurs. The mechanism appears to be related to that occurring in the Fischer-Tropsch reaction. After hydrogenation the reaction cycle can be repeated. Methane addition to ethene, propene, and acetylene is demonstrated to occur using silica-supported ruthenium and cobalt catalysts. With 13CH4 it was shown that propane and butane are formed both by self-homologation of ethene and propene, respectively, as well as by methane incorporation. Carbon scrambling according to the metathesis reaction is very slow.

Fischer-Tropsch synthesis, transition metal surfaces, CO and CH~ reactivity, electronic features in F-T synthesis, bond strength, activation energy, chemisorption, CO dissociation, extended Hiickel method, ASED method, quantum chemistry.The electronic features determining the reactivity of CO and CH x on transition metal surfaces are reviewed. Focus is on the relevant features that control the Fischer-Tropsch synthesis. The CO dissociation reaction path is controlled by the interaction with the CO bond strength weakening 2~r* orbitals. CH 3 fragment adsorption is controlled by o type molecule fragment orbitals. This directs the CH 3 fragment to the atop adsorption site on those late transition metals that have strongly interacting d-valence electrons. Adsorbed C and O have a stronger bond strength than CH 3 because they have also unoccupied atomic p orbitals available to bonding. Because the bond strength of adsorbed C and O increases more rapidly with depletion of d-valence electron occupation than that of CO, the activation energy for CO dissociation decreases for the corresponding transition metals towards the left of the periodic system. The rate of methanation versus chain growth is controlled by the strength of the M-CH 3 bond versus the activation energy of carbon-carbon bond formation. The first appears to be more sensitive to variations in metal carbon bond strength than the latter.