Ru-M (M = Fe or Co) Catalysts with high Ru surface concentration for Fischer-Tropsch synthesis

Ru-Co/Al2O3 and Ru-Fe/Al2O3 have been prepared by the reduction-deposition method. This approach favours the interaction between Ru and Fe or Co in the final catalysts, while increasing surface enrichment of Ru. Their performance for the Fischer-Tropsch Synthesis (FTS) has been evaluated in a fixed bed reactor. Ru-Co/Al2O3 displays the highest activity in the series, doubling the steady-state CO conversion rate of a Ru/Al2O3 catalyst with 3 times higher Ru loading. Ru-Fe/Al2O3 displays higher initial CO conversion and -CH2- productivity than Ru/Al2O3, but its activity declines during operation reaching lower conversion rates than Ru/Al2O3. In addition to CO2, Ru-Fe/Al2O3 produces oxygenated products, mainly alcohols. To a lesser extent, the formation of oxygenates over Ru-Co/Al2O3 and Ru/Al2O3 is also observed, and ascribed to the small crystallite size of the Ru particles. The evolution of CO2 during time on stream indicates that Fe is segregated to the surface of this catalyst during the FTS.