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In a complex reaction system, in which gas, liquid, and solid catalysts work together, understanding the impact of mass transfer that varies with the catalyst pore structure is very challenging but also essential to designing selective catalysts.

In this article, the hydrothermal stability and change in the physicochemical properties of supported cobalt catalysts modified with Zn, P, and Zr have been studied for slurry‐phase Fischer–Tropsch synthesis (FTS) at 230°C and 2.0 MPa. The Co/P/γ‐Al2O3 exhibited weaker interactions between cobalt oxides and alumina support than other catalysts. The support of all the Co catalysts underwent phase transformation of γ‐Al2O3 into boehmite (AlO(OH)) during hydrothermal treatment at 250°C for 12 h, except Co/P/γ‐Al2O3, which was hydrothermally stable in the presence of H2O. The initial CO conversion increased with increasing number of Co surface sites during FTS. However, CO conversion decreased when H2O was cofed, causing a shift in product distribution from C2–C4 to C5+ hydrocarbons. The CO conversion and product distribution were partially reversible at 0–42.7% H2O in the feed stream. The lower adsorption capacity of H2O on the catalysts caused higher CO conversions under H2O‐rich condition. The catalytic activity of Co/P/γ‐Al2O3 was least affected by the co‐fed H2O, while that of Co/Zr/γ‐Al2O3 was strongly influenced by H2O concentration in the feed stream. The Co/P/γ‐Al2O3 did not exhibit phase transformation of γ‐Al2O3 to AlO(OH) during slurry‐phase FTS.

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