Steady-state isotopic transient kinetic analysis of the Fischer-Tropsch synthesis reaction over cobalt-based catalysts

The paper presents a transient kinetic anal. of the Fischer-Tropsch synthesis reaction by using the SSITKA technique in combination with a gas-chromatograph-mass-spectrometer (GCMS) anal. of the 13C-labeled and 18O-labeled hydrocarbon and alc. reaction products. Expts. are performed on a Co/Ru/TiO2 catalyst and a fully metallic Co-sponge model catalyst at 498 K and 1.2 bar. The exptl. results are discussed in a qual. way to obtain mechanistic information. The Co-sponge catalyst is used to study alc. formation, since the TiO2 support disturbs the measurements on the Co/Ru/TiO2 catalyst. The formation of hydrocarbons proceeds via a two-pool mechanism, where two carbon pools contribute to methane formation and C-C coupling. Paraffins and olefins are both primary products, but the GCMS anal. demonstrates that readsorption of 1-olefins is an important step. The readsorption of iso- and 2-olefins is of less importance. The steady-state performance of the catalyst indicates the presence of a physisorbed hydrocarbon layer, even under process conditions where no wax build-up in the catalyst pores occurs. Although the Anderson-Schulz-Flory distribution gives rise to assume chain-length independence of the surface reactions starting at C3, this does not hold when discrimination between the paraffins and the olefins is made. Alc. formation can be considered as a termination reaction that occurs via a CO insertion or a CHxO insertion mechanism. [on SciFinder (R)]