Formation of hydrocarbons via CO2 hydrogenation – A thermodynamic study

• Calculation of the thermodynamic equilibria of the direct CO2 Fischer–Tropsch.
• Overall CO2 conversion increases by increasing the H2:CO feed ratio.
• Hydrogen yield into hydrocarbons is maximized at temperatures below 600 K.
• In situ removal of water does not affect the overall conversion or selectivity.
• Termination step in product formation is thermodynamically favourable.

The thermodynamic equilibria of the synthesis of hydrocarbons via CO2 reduction and the Fischer–Tropsch (FT) process have been calculated minimizing the Gibbs free energy. This study reveals the theoretical optimum reaction conditions for the tandem process: CO2 reduction followed by the FT conversion into hydrocarbons in order to (i) increase the overall CO2 conversion (by increasing the H2:CO2 ratio), (ii) increase the hydrocarbon formation (increasing the H2:CO2 ratio or addition of CO in the feed mixture) and (iii) maximize the H2 yield into hydrocarbons formation as opposed to water (when the reaction temperature is below 600 K or by the addition of CO in the feed mixture). In situ removal of water has no apparent effect on the overall conversion or hydrogen selectivity in the tandem system. These equilibrium calculations, in conjunction with catalysis development and reaction engineering are expected to guide the future research approach towards CO2 utilization.