Three Fe catalysts with different Na contents were prepared, characterized, and investigated for the CO 2 -based Fischer-Tropsch synthesis (FTS). The FTS results clearly indicated that the selectivity towards long-chain hydrocarbons was driven by the surface Na content, which promotes the CO dissociation and chain propagation. Additionally, it was shown that Fe 3 O 4 , Fe 5 C 2 and Fe 7 C 3 coexist during FTS, revealing specific catalytic activity. As a result, a tandem mechanism was suggested for the CO 2 conversion, consisting in a reverse water-gas shift on Fe 3 O 4 followed by CO hydrogenation on the Fe carbides.