Sustainable Fuels from CO2-rich synthesis gas via Fischer-Tropsch technology

CO2-containing synthesis gas is a relevant feedstock for the production of synthetic fuels using Fischer-Tropsch Synthesis. We report the role of CO2 in CO2, CO and H2 mixed feeds over a cobalt-based catalyst at 220 °C and 21 bar in a packed bed reactor. The C5+ selectivity remains above 78 % even for CO2-rich synthesis gas with 75 % CO2/(CO+CO2). Using 13CO2 isotopic labeling, the increase in methane selectivity is attributed to both CO and CO2 methanation, which is limited by maintaining a H2/CO outlet ratio below 10 and an outlet CO partial pressure above 0.2 bar, respectively. Operando modulated DRIFTS confirms a positive relationship between CO surface coverage and CO partial pressure. From DFT and microkinetic modeling, enhanced CO and CO2 methanation could be attributed to a lower CO surface coverage and a higher H2 surface coverage. This work identifies boundaries for efficient cobalt-catalyzed mixed-feed FTS for synthetic fuels production.