The Effect of Water on the Activity and Selectivity for Carbon Nanofiber Supported Cobalt Fischer–Tropsch Catalysts

The effect of water on the activity and selec- tivity for a series of carbon nanofiber supported Fischer- Tropsch cobalt catalysts has been investigated. Fischer- Tropsch synthesis was carried out in a fixed bed reactor at industrially relevant conditions (483 K, 20 bar, H2/ CO = 2.1). Three catalysts were prepared either by incipient wetness impregnation or wet impregnation and consisted of 12 or 20 wt% cobalt deposited on carbon nanofibers of the platelet and fishbone structures. Addition of 20 and 33 mol% water to the reactor inlet increased the reaction rates, but also the deactivation rates of all the catalysts. As a result of the high water concentrations, the catalysts were irreversibly deactivated. A positive corre- lation between the amount of water in the reactor and the selectivity to long-chain hydrocarbons (C5?) was found.