On the performances of highly promoted Fe-Zn-Cu-K catalysts for CO2 Fischer-Tropsch synthesis

A state-of-the-art Fischer-Tropsch 100Fe:10Zn:1Cu:4 K catalyst and catalysts promoted with higher Cu and K loadings were compared in terms of activity, selectivity and stability in the CO₂ Fischer-Tropsch synthesis. Higher promoter loadings increased selectivity towards heavier hydrocarbons, with a minor impact on activity at high conversion conditions. In such conditions, both catalysts samples experienced activity loss possibly due to iron carbide oxidation at high water partial pressure, but while the state-of-the-art catalyst had also selectivity affected, the highly promoted catalyst preserved heavy products selectivity. Notably, the highly promoted catalyst could be successfully rejuvenated in-situ by decreasing pressure and increasing temperature under CO₂/H₂ flow. This procedure allowed to restore almost completely the initial activity while preserving an excellent C₂₊ hydrocarbon selectivity. On the contrary, the traditional Fischer-Tropsch catalyst, after the same rejuvenation treatment, showed a more pronounced selectivity shift towards lighter products. These findings can help in formulating stable catalysts that promote the one-pot synthesis of long chain hydrocarbons from CO₂ at industrially relevant conditions.