Fig. 1.

Gibbs free energy generation through independent a) CO and b) H₂/CO₂ catabolism for ethanol production. The dashed lines indicate where $\mathrm{\Delta }{G}_{\text{cat}}^{0^{\prime }}$ = – 15 kJ mol⁻¹_CS. H₂/CO₂ catabolism is cut-off at $\mathrm{\Delta }{G}_{\text{cat}}^{0^{\prime }}$ = 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