Mechanism of CO2 and H+ reduction by Ni(cyclam)(+) in aqueous solution. A pulse and continuous radiolysis study

The reduction of CO2 and H+ by Ni(cyclam)(+) in aqueous solution was found to proceed by the reduction of Ni(cyclam)(CO2)(+) or Ni(cyclam)(H)(2+) by N i(cyclam)(+). At ambient temperature the rate constants for the bimolecular reactions are 1.6 x 10(8) and 7.2 x 10(7) M-1 s(-1), respectively. Continu ous gamma-radiolysis studies have demonstrated nearly quantitative formatio n of CO from two Ni(cyclam)(+) at pH 5.2 under 1 atm of CO2 and in the pres ence of formate. Under the same conditions, but at low CO2 concentration, t he reduction of protons was found to compete with CO2 reduction.