Mechanistic pathway for C2+ hydrocarbons over an Fe/K catalyst

Our mechanism for the methanation reaction pathway (Govender et al., 2008) during the Fischer–Tropsch synthesis at high-temperature reaction conditions (330 °C, H2/CO = 15 and 1.2 bar) is extended here to account for the formation of C2+ hydrocarbons. The C2 and C3 hydrocarbon transients derived from 13CO SSITKA experiments were used to discriminate between three mechanistic models. It is shown that a mechanism with two surface intermediates for the C2+ hydrocarbons and with olefin readsorption directly to the corresponding paraffin surface intermediate describes the data the best. Parameter estimates for the rate constants describing the formation of the C2 are reported. The optimal model is also shown to fit the C3 hydrocarbons. The SSITKA measurements were also used to determine surface coverages and the turnover frequency. We propose Cs and CsH as the active C1 species with both participating in chain initiation to form reactive C2 species such as CsCsH.