| Synthesis gas, derived from steam gasification of coal, reacts in the presence of various metallic catalysts to produce both gaseous and liquid hydrocarbons. The mechanism of carbon monoxide hydrogenation in two different catalytic systems was investigated. First, in a slurry reactor, the mechanism of hydrocarbon chain propagation on a heterogeneous cobalt Fischer-Tropsch catalyst was delineated by studing the effect of reaction media on the product distribution. Second, the mechanism of homogeneous catalytic methanol homologation was probed by stoichiometrically examining the kinetics of the rate-determining methyl transfer reaction.; The probability of propagation, (alpha), of a surface bound hydrocarbon species on a 39% cobalt on kieselguhr Fischer-Tropsch catalyst was demonstrated to be slightly effected by the surrounding medium. As the polarity of the surrounding medium was increased, (alpha) also increased: gas phase ((alpha) = 0.78), decalin ((alpha) = 0.80), dodecane ((alpha) = 0.82), ethanol ((alpha) = 0.86), 2,2,2-trifluoroethanol ((alpha) = 0.87), p-dioxane ((alpha) = 0.90), N,N-dimethylformamide ((alpha) = 0.93). However, based on organometallic analogues, this relatively small effect is insufficient to support a carbon monoxide insertion mechanism for Fischer-Tropsch chain propagation. The methylene polymerization mechanism of chain growth is consistent with the data, on the condition that the probability of chain termination is slightly enhanced in less polar media.; The stoichiometric methyl transfer reaction from a methyl quaternary ammonium cation to metal carbonyl anions was investigated as a model for the rate-determining step in the homogeneous catalytic homologation of methanol. The second-order nucleophilic substitution reaction was demonstrated to be first-order in both {lcub}MeNR(,3)('+){rcub} and {lcub}HFe(CO)(,4)('-){rcub} and zero-order in P(,CO) and P(,H(,2)). In the temperature range of 180(DEGREES)-210(DEGREES)C using N-methyl pyrrolidinone as a solvent, thermodynamic activation parameters were determined ((DELTA)H('(NOT=)) = 44.1 kcal/mole, (DELTA)S('(NOT=)) = +16.6 eu). The rate of the methyl transfer reaction was observed to increase with decreasing dielectric constant and with decreasing salt concentration. In the {lcub}MeNR(,3){rcub}{lcub}Mn(CO)(,5){rcub} system the product selectivity to ethanol and methane was independent of P(,CO) and P(,H(,2)) but dependent on the Mn(CO)(,5)('-) concentration. At 200(DEGREES)C and 3600 psig of 3:1 CO/H(,2) the difference in second-order rate constants (1.99 x 10('-4)M('-1)s('-1) for HFe(CO)(,4)('-) and 5.31 x 10('-4)M('-1)s('-1) for Mn(CO)(,5)('-)) is an indication of the relative nucleophilicity of the metal carbonyl anions. The difference in product selectivity between the two metal systems is attributed to the difference in intra- versus inter-molecular elimination of products. |
