Enzyme-catalyzed sequential reduction of carbon dioxide to formaldehyde

It has been reported that enzymatic-catalyzed reduction of CO₂ is feasible.Most of literature focuses on the conversion of CO₂ to methanol.Hereinwe put emphasis on the sequential conversion of CO₂ to formaldehyde and its single reactions. It appears that CO₂ pressure plays a critical role and higher pressure is greatly helpful to form more HCOOH as well as HCHO. The reverse reaction became severe in the reduction of CO₂ to formaldehyde after 10 h, decreasing HCHO production. Increasing the mass ratio of formate dehydrogenase to formaldehyde dehydrogenase could promote the sequential reaction. At concentrations of nicotinamide adenine dinucleotide lower than 100 mmol·L^-1, the reduction of CO₂ was accelerated by increasing cofactor concentration. The optimum pH value and concentration of phosphate buffer were determined as 6.0 and 0.05 mol·L^-1, respectively, for the overall reaction. It seems that thermodynamic factor such as pH is restrictive to the sequential reaction due to distinct divergence in appropriate pH range between its single reactions.