Fig. 1

Gibbs free energy generation through independent a) CO and b) H₂/CO₂ catabolism for ethanol production. The dashed lines indicate where \(\Delta G_{\text{cat}}^{{0^{\prime}}}\) = – 15 kJ mol ⁻¹_CS . H₂/CO₂ catabolism is cut-off at \(\Delta G_{\text{cat}}^{{0^{\prime}}}\) = 0, where the catabolic reaction would be at equilibrium and no energy could be released from it; the white region represents the gas concentrations where the inverse reaction (H₂/CO₂ production from ethanol) would be spontaneous