Preferential chemical vapor deposition of ruthenium on cobalt with highly enhanced activity and selectivity for Fischer–Tropsch synthesis

• Ru is preferentially deposited on Co of Co/γ-Al2O3 by CVD of ruthenocene for FTS.
• As Ru in RuCo/γ-Al2O3 increases, SBET increases and dcobalt crystallites decreases.
• Ru facilitates cobalt oxides reduction and suppresses cobalt aluminate formation.
• Ru enhances up to 2.8 times CO conversion and 30% C5+ selectivity.

Various amount of ruthenium was preferentially deposited on cobalt of Co/γ-Al2O3 by chemical vapor deposition (CVD) of ruthenocene and compared with a CoRu/γ-Al2O3 catalyst prepared by the usual impregnation method for Fischer–Tropsch synthesis (FTS). The Co/γ-Al2O3 was prepared by wet impregnation of cobalt nitrate aqueous solution, and then dried and calcined at 400 °C for 4 h. Ruthenocene was sublimated, carried by argon, and then mixed with H2 and passed over γ-Al2O3 or calcined Co3O4/γ-Al2O3 catalyst at various temperatures. The effluent gasses were passed through a gas cell of FTIR to determine the ruthenocene thermo-chemical decomposition products. In a temperature range (window) of 150–200 °C the ruthenocene decomposes on Co3O4/γ-Al2O3 but not on γ-Al2O3. The catalysts were characterized by TPR, EDX, TEM, XRD and BET. The FTS activity and selectivity of the Ru-Co/γ-Al2O3 catalysts were investigated in a fixed bed microreactor. The preferential CVD of 0.3 wt% ruthenium onto 15.0 wt% Co/γ-Al2O3 (CoRu5-180) catalyst shifted both cobalt TPR peaks by about 120 °C to lower temperatures, showed about 2.8 times higher conversion, 30% more C5+ selectivity, and 30% less selectivity of methane. The CoRu5-180 catalyst showed about 81% higher CO conversion and 12% higher selectivity to C5+ than the same catalyst composition prepared by the used impregnation of ruthenium chloride onto the 15.0 wt% Co/γ-Al2O3.

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