TITLE: Fischer--Tropsch Synthesis over a Ruthenium Catalyst: Infrared and Kinetic Studies.

AUTHOR: J. G. Ekerdt.

INST.  AUTHOR: California Univ., Berkeley. Lawrence Berkeley Lab.

SPONSOR: California Univ., Berkeley. Dept. of Chemical Engineering.*Department of Energy.


PUB.  TYPE: Technical Report

PUB.  COUNTRY: United States

SOURCE: Department of Energy [DE],  Apr 79,  117p.


The synthesis of hydrocarbons from CO and H sub 2 was studied on a silica-supported Ru catalyst and the species present on the catalyst surface were characterized by infrared spectroscopy. The synthesis of ethane, propylene, and propane, the principle products observed in addition to methane, were favored at high CO partial pressures, low H sub 2 /CO ratios, and low temperatures. Evidence obtained from the combined infrared and kinetic studies suggests that the first stage of reaction involves the dissociation of CO to produce surface carbon atoms.  Hydrogenation of the surface carbon to ethane and propane in the absence of chemisorbed CO suggests that chain propagation does not involve CO insertion into a metal-alkyl type intermediate. In an attempt to identify reaction intermediates, ethylene and cyclohexene were added to the synthesis gas feed. In the case of ethylene enhanced yields of propylene were observed. When cyclohexene was used as a scavenger, a series of alkyl cyclohexene and alkyl cyclohexane products were obtained. The results of both experiments suggest that alkylidene groups are present on the catalyst surface. Reaction mechanisms for the formation of methane are developed and used to formulate methanation rate expressions consistent with the experimental observations. In addition, reaction mechanisms for the formation of higher molecular weight olefins and alkanes are proposed which incorporate the postulated alkylidenes in chain growth as well as chain termination steps. (ERA citation 04:044231)