The effect of CO2 on a cobalt-based catalyst for low temperature Fischer–Tropsch synthesis

A series of Fischer–Tropsch synthesis (FTS) experiments, which entailed repeatedly switching between a CO (CO/H2/N2) and a CO2 (CO2/H2/N2) feed, were conducted in a fixed bed reactor over a cobalt-based catalyst. It is worth noting that the effect of the CO2 on the properties of a cobalt-based catalyst was very small under the reaction conditions we chose. There was no apparent catalyst deactivation at reaction temperatures of 180 °C and 200 °C when we continually alternated between the CO and CO2 feeds.We observed dramatic changes in the catalyst activity and product selectivity for CO2 hydrogenation before and after the initial FTS for CO feed at 180 °C. In addition, during the initial CO hydrogenation on the cobalt catalyst, both the olefin and paraffin formation rates suddenly changed from one pseudo-stable state to another. These differences may have been caused by liquid products, whether deposited on the catalyst surface or in the catalyst pores during CO FTS.A mild catalyst deactivation was observed at the operating temperatures of 210 °C and 220 °C, respectively. According to the comparison we made between the conversion of the feed gases and the product formation rates for paraffin and olefin, and our speculations concerning possible side reactions, we conclude that the catalyst deactivation is possibly attributable to the re-oxidation by water.

► Both CO and CO2 were readily hydrogenated on a cobalt-based catalyst.
► The effect of the CO2 on the catalyst deactivation for FTS was very small.
► The catalyst deactivation was attributable to the re-oxidation by water.
► The accumulation of liquid products changed the catalyst activity and product selectivity.