Fischer–Tropsch synthesis: Effect of CO2 containing syngas over Pt promoted Co/γ-Al2O3 and K-promoted Fe catalysts

The effect of CO2 was studied for cobalt and iron Fischer–Tropsch (FT) synthesis. CO2 behaves differently in the presence of CO over cobalt and iron catalysts in terms of hydrogenation. A systematic increase of the CO2 mole fraction of carbon in the feed gas mixture alters the product distribution dramatically for cobalt FT synthesis with CO2 behaving like an inert gas at higher partial pressure of CO. With cobalt, CO appears to compete with CO2 for adsorption. Using an iron FT catalyst, hydrogenation of CO2 was effected due to the presence of the reverse water–gas shift activity of the catalyst which converts CO2 to hydrocarbons through the formation of CO. Unlike the cobalt catalyst, the product distribution was only slightly altered with increasing CO2 content in the feed gas mixture to the iron catalyst. This difference in behavior of CO2 over cobalt and iron could be attributed to the absence of reverse water–gas shift activity on cobalt and hydrogenation of CO2 to hydrocarbons—other than methane—will be derived through the formation of CO.

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► CO2 affects the cobalt and iron FT synthesis differently.
► CO appears to compete with CO2 for adsorption on cobalt.
► Hydrogenation of CO2 on cobalt produces mainly methane.
► CO2 altered only slightly the product distribution of Fe-FT synthesis.
► For low-temperature FT, the CO2 acts primarily as a diluent.