ESTIMATES OF RATE COEFFICIENTS FOR ELEMENTARY PROCESSES OCCURRING DURING FISCHER-TROPSCH SYNTHESIS OVER RU TIO2

The dynamics of elementary processes involved in Fischer-Tropsch synthesis of hydrocarbons over Ru/TiO2 have been determined from the analysis of data from both steady-state and transient-response experiments. Both types of experiments were carried out with different feed catalyst bed residence times to assess the effects of olefin readsorption on the dynamics of chain initiation, propagation, and termination. Strong evidence was found for the rapid reentry of ethylene into the chain growth process. The reentry of C3+ olefins, though, is negligible for the conditions studied. The holdup of hydrocarbons in a weakly physisorbed state was found to be significant for C6+ products and must be accounted for in the simulation of transient-response experiments. When the effects of ethylene readsorption and C6+ holdup are properly taken into account, the rate coefficients for chain initiation, propagation, and termination, determined from simulations of the transient-response experiments, are independent of carbon number and catalyst-bed residence time. Rate coefficients for the readsorption of ethylene, the depolymerization of adsorbed ethyl groups, and the dehydrogenation of methyl to methylene groups were also determined from simulations of the transient-response experiments. (C) 1994 Academic Press, Inc.