Fischer Tropsch synthesis from H2-deficient biosyngas over Mn added Co/SiO2 catalysts

• Adding 0.8 wt.% Mn to Co/SiO2 increased the small-sized Co reduction.
• High CO conversion of 52.6% using H2-deficient biosyngas over Co-(0.8%)Mn/SiO2 was obtained.
• 7.0 vol% CO2 in the feed gas inhabited CO2 formation during FTS.
• Relatively slow CO2 hydrogenation rate decreased its conversion, compared with CO conversion.
• FTS from H2-deficient gas may be efficient, due to avoiding of gas composition adjustment steps.

Co/SiO2 catalysts with 0.4–7.0 wt.% of Mn addition were prepared and evaluated for Fischer–Tropsch synthesis (FTS), using H2-deficient biosyngas (H2/CO/CO2/N2 = 45/45/7/3, vol%) as feed gas. 0.8 wt.% of Mn addition to Co/SiO2 increased Co dispersion and weakened Co–Si interaction on Co–(0.8%)Mn/SiO2 catalyst. Co reducibility was improved to 32.1% and 79.3% at 150–400 °C and 150–750 °C respectively by H2-temperature programmed reduction (TPR), which resulted in CO conversion of 52.6% and C5+ yield of 43.6% at 24 h time on stream when H2-deficient biosyngas was used as feed gas for FTS. Co was further dispersed with low reducibility at higher Mn addition amount, which decreased CO conversion and favored gaseous hydrocarbon synthesis over Co–(2.0%)Mn/SiO2 and Co–(7.0%)Mn/SiO2. The higher H2/CO usage ratio was obtained over Co/SiO2 using H2-deficient biosyngas, compared with that using feed gas with H2/CO ratio of 2.0 over the same catalyst. The existence of small amount of CO2 (like 7.0 vol%) in biosyngas might be the main reason to inhibit water gas shift reaction and impel CO2 conversion.