On the effect of water on the Fischer–Tropsch rate over a Co-based catalyst: The influence of the H2/CO ratio

The effect of water partial pressure on the Fischer–Tropsch (FT) rate of a cobalt catalyst supported on narrow-pore γ-Al2O3 was investigated at industrially relevant process conditions (483 K, 30 bar, pellet size: 53–90 μm). Inlet water partial pressure was varied up to 9 bar by external water vapour addition at different H2/CO molar ratios ranging from 1 to 3.The effect of water was found to be positive on FT-rate independently of the H2/CO ratio, but more significantly at H2-poor condition.Temperature-programmed hydrogenation (TPH) was used to verify the presence of unreactive carbon species on the catalyst after 22 h on stream at the different conditions with and without exposure to about 9 bar water. A higher temperature feature that could be associated to amorphous polymeric carbon was detected at H2-poor conditions but remained unchanged upon 2 h of water exposure which did not result in a change in the amount of amorphous polymeric carbon detectable by TPH.

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► Water has a positive kinetic effect during FTS for narrow pore γ-Al2O3-supported Co-catalyst at H2/CO ranging from 1 to 3.
► Unreactive carbon forms in FTS at H2/CO = 1 after 1 day on stream; no unreactive carbon is detected at stoichiometric and H2-rich conditions.
► Water co-feeding does not change the amount of unreactive carbon visible by temperature programmed hydrogenation on a spent catalyst.