Feed composition modulation of hydrocarbon synthesis over a cobalt oxide catalyst

Studies of the Fischer‐Tropsch reaction over a cobalt catalyst under unsteady‐state conditions (i.e. both step‐change and forced feed composition cycling or feed modulation) have been carried out. Conversions were differential under conditions of atmospheric pressure and 473 K. The steady‐state rate versus feed composition curves for the alkanes were generally skewed towards the rich‐hydrogen feed compositions, while the olefins exhibited maximum steady‐state rates at the stoichiometric feed reactant ratio. The adsorption of hydrogen in the initiation step or hydrogenation of an unsaturated surface species appeared to be important in determining the alkane formation rates. The appearance of overshoot in the transient responses for some products conforms to the interpretation of a hypothesis of a succession of steady‐state rates on the surface. However, a closer examination of overshoot behaviour suggests that there is participation of carbon from within the catalyst bulk. Significant improvements found for the time‐average rates of some products were consistent with the results of the step‐change experiments.