The interaction of CO, H 2 and ethylene over a typical cobalt-based Fischer-Tropsch synthesis catalyst

Co-feeding ethylene to a Fischer-Tropsch synthesis (FTS) reactor exhibited multiple-effects, depending on the reaction conditions. Co-feeding a small amount resulted in a significant improvement in catalytic performance; however, both CO reactivity and chain-growth probability decreased when increasing ethylene concentration at a high temperature. This may be due to the "H-scavenging effect". Co-feeding CO into the ethylene hydrogenation system suppressed ethylene reactivity, which was seen as evidence of the CO "occupancy effect". This effect was dominant at low reaction temperatures, but weaker at high reaction temperatures. Both the CO "occupancy effect" and the "H-scavenging effect" of ethylene had a significant impact on the chain-growth reaction pathways. A new mechanism called the "ethylene-assisted CO-insertion mechanism" was hypothesised to explain the ethylene promotional effects on FTS. This mechanism may co-exist with both the CO-dissociation type mechanism and the ethylene hydrocracking chain-growth mechanism, and may allow the FTS product distribution to be tuned.