Mechanism of CO₂ and H⁺ Reduction by Ni(cyclam)⁺ in Aqueous Solution. A Pulse and Continuous Radiolysis Study

The reduction of CO 2 and H + by Ni(cyclam) + in aqueous solution was found to proceed by the reduction of Ni(cyclam)(CO 2 ) + or Ni(cyclam)(H) 2+ by Ni(cyclam) + . At ambient temperature the rate constants for the bimolecular reactions are 1.6 × 10 8 and 7.2 × 10 7 M - 1 s - 1, respectively. Continuous γ-radiolysis studies have demonstrated nearly quantitative formation of CO from two Ni(cyclam) + at pH 5.2 under 1 atm of CO 2 and in the presence of formate. Under the same conditions, but at low CO 2 concentration, the reduction of protons was found to compete with CO 2 reduction.