THE MECHANISM AND KINETICS OF FISCHER-TROPSCH SYNTHESIS OVER SUPPORTED RUTHENIUM CATALYSTS

A detailed study of the kinetics of the Fischer-Tropsch synthesis of hydrocarbons, methanol, and acetaldehyde, over alumina- and silica-supported ruthenium catalysts has been carried out over a broad range of reaction conditions. Based on these results and information taken from the literature, mechanisms for the formation of normal paraffins, (alpha)-olefins, methanol, and acetaldehyde have been proposed.; Rate data were obtained between 448 and 548K, 1 and 10 atm, and H(,2)/CO ratios between 1 and 3, utilizing a micro flow reactor operated at very low conversions. These conditions allowed the intrinsic reaction kinetics to be observed with minimal interference from secondary reactions. In addition to the studies performed with H(,2)/CO mixtures, a series of experiments were carried out utilizing D(,2)/CO mixtures. These studies were used to help identify rate limited steps and steps that were at equilibrium.; A complementary investigation, carried out by in situ infrared spectroscopy, was performed using a Fourier Transform spectrometer. The spectra obtained were used to identify the modes of CO adsorption, the CO coverage, and the relative reactivity of different forms of adsorbed CO. It was established that CO adsorbs on alumina-supported Ru in, at least, two forms: (i) Ru-CO and (ii) OC-Ru-CO. Only the first of these forms participates in CO hydrogenation. The coverage of this species is described by a simple Langmuir isotherm.; The kinetics of hydrocarbon synthesis, the olefin to paraffin ratio for each product, and the probability of chain propagation can all be interpreted on the basis of the reaction mechanism described below. Reaction is initiated by the adsorption of CO and its subsequent dissociation. Atomic oxygen is rejected as H(,2)O and the carbon undergoes stepwise hydrogenation to form CH(,x)(x = 1-3) species. Methane is formed by reductive elimination of methyl groups while the formation of higher molecular weight products is initiated by the addition of a CH(,2) unit to an adsorbed CH(,3) group. Further chain growth then proceeds via a similar process. Olefins are formed by (beta)-elimination of hydrogen from an adsorbed alkyl group and paraffins are formed by reductive elimination of an alkyl group. Rate expressions based on this mechanism are reasonably consistent with the experimental data. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI...