Water is an inherent component in Fischer–Tropsch synthesis on Co catalysts, and the effect of water is discussed with an emphasis on alumina and aluminates as support materials. Water may affect the selectivity, activity, deactivation, and state of the catalyst, and without exception, water is known to enhance the C5+ selectivity by increasing the chain propagation α value. The effect of water depends on the catalyst. Small-pore γ-Al2O3 is less efficient at high water content than large-pore γ-Al2O3. The effect of water on selectivity is independent of its origin: i.e., adding water to the feed has the same effect as water produced by the reaction. Arguments are provided for the effect of water being partially mechanistic in nature and occasionally due to pore condensation. In particular, we introduce water-assisted CO activation to methylidyne as an option for generation of polymerization monomers. An additional factor that needs to be considered is that high water partial pressure is concurrent with reduction in hydrogen partial pressure. The influence of water strongly depends on the type of reactor employed
