A novel photosynthetic mimic reaction catalysed by K[Ru(H-EDTA)Cl] · 2H2O; reduction of carbon dioxide to formate and formaldehyde in the presence of an aqueous suspension of Pt—CdS—RuO2

An efficient photocatalytic reduction of carbon dioxide to HCOOH and HCHO is reported using KRu(H-EDTA)Cl] · 2H₂O (1) as homogeneous catalyst and particulate Pt—CdS—RuO₂ as photon absorber at 505 nm. This system produces 0.22 M of HCOOH and 0.10 M of HCHO in 6 h of photolysis at rates of 3.05 × 10⁻² M h⁻¹ and 2.0 × 10⁻² M h⁻¹ respectively. Trace amounts of CH₃OH, CH₄ and CO are detected in the reaction vessel. The rates of formation of HCOOH and HCHO exhibit a first-order dependence on the catalyst and dissolved CO₂ concentrations. The reaction shows deuterium isotope effects (k_H/k_D) of 1.5 and 2.00 for the formation of HCOOH and HCHO respectively. Under identical experimental conditions, the rate of decomposition of formate was studied. The rate of decomposition of formate is slower (by two orders of magnitude compared with the formation of formate) even at high formate concentrations. A mechanism for the formation of HCOOH and HCHO is proposed.