What are the advantages and disadvantages of cobalt and iron catalysts in Fischer-Tropsch synthesis?

Cobalt-based systems first have low methane selectivity but high selectivity for the target product. Furthermore, it has good physical strength, which results in low losses during operation; the cost of catalyst per ton of product is low, liquid-solid separation is easy, and it is highly environmentally friendly. However, it is highly sensitive to sulfur and prone to sulfur poisoning, so only syngas produced from natural gas can be used as a raw material. Iron-based catalysts require a low sulfur content and have low manufacturing costs; they are suitable for coal-to-syngas production. However, their drawback is high catalyst loss per ton of product, and their selectivity is lower than that of cobalt-based catalysts.

Metals such as iron, cobalt, nickel, ruthenium, and rhodium all exhibit catalytic activity in the Fischer-Tropsch synthesis reaction. However, due to the drawback of nickel in producing large amounts of methane and its tendency to undergo carbonylation, as well as the high cost of ruthenium and rhodium, they are not suitable for large-scale industrial use. Therefore, only iron-based and cobalt-based catalysts have been widely applied in industry to date. There are significant differences in the selectivity and product distribution of the Fischer-Tropsch synthesis reaction across different catalysts. The hydrogenation activity of cobalt catalysts is generally higher than that of iron-based catalysts; therefore, the F-T synthesis products using cobalt catalysts contain a higher proportion of saturated hydrocarbons ； As the temperature increases, the increase in methane selectivity also occurs more rapidly than with iron catalysts. Iron-based catalysts can be used in high-temperature Fischer-Tropsch synthesis reactions at 310–350°C, whereas in this temperature range, the methane selectivity of cobalt-based catalysts is close to 100%. Under normal circumstances, the selectivity for oxides of cobalt-based catalysts is also lower than that of iron-based catalysts. Iron-based catalysts exhibit strong conversion activity, whereas cobalt-based catalysts have virtually no catalytic activity for the conversion reaction. Therefore, when using cobalt-based catalysts, the H2/CO ratio at the reactor inlet should be close to its consumption ratio; whereas with iron-based catalysts, the presence of the conversion reaction allows for the adjustment of the reactant composition, so the H2/CO ratio at the reactor inlet does not necessarily need to be close to its consumption ratio