Copper-Catalyzed Radiolytic Reduction of CO2 to CO in Aqueous Solutions

Published

May 1, 2001

Author(s)

J Grodkowski, Pedatsur Neta

Abstract

Radiolysis of aqueous solutions containing CO₂ and Cu(II) ions under reducing conditions leads first to reduction of the Cu(II) and then to formation of CO. Experiments under various conditions show that although Cu(II) was often reduced to colloidal Cu(0) particles, formation of CO requires the presence of Cu(I), not Cu(0). It also requires that CO₂ be first reduced to the CO₂^- radical. The CO₂^- radical was produced radiolytically by reaction of CO₂ with e_aq^- or by reaction of formate ions with H and OH radicals and photochemically by reaction of formate with the acetone triplet. The CO₂^- radicals are reduced to CO via addition to Cu(I) and subsequent reaction of the product with another Cu(I). The first reaction produces CuCO₂, which undergoes protonation at pH < 4. The reaction of the neutral CuCO₂ with Cu(I) leads to reduction of the copper to form Cu₂⁺ and subsequently Cu(0) particles. However, the reaction of the protonated form, CuCO₂H⁺, with Cu(I) leads to oxidation of the copper and formation of CO in the form of the CuCO⁺ complex. After most of the copper is converted into CuCO⁺ subsequent reactions involve this species instead of Cu⁺ and lead to further production of CO. From pulse radiolysis measurements, the rate constants for the reactions of the CO₂^- radicals with Cu⁺ and CuCO⁺ were found to be approximately equal}1 x 10⁹ and 1.5 x 10⁸ L mol^-1 s^-1, respectively. The protonated adduct formed by the latter reaction at pH 3.4, Cu(CO)CO₂H⁺, reacts with CuCO⁺ with a rate constant k approximately equal} 5 x 10⁵ L mol^-1^ s^-1^. It also undergoes first order decomposition and second-order decay.

Citation

Journal of Physical Chemistry B

Volume

105

Issue

No. 21

Pub Type

Journals

Keywords

carbon dioxide, carbon monoxide, copper colloids, copper ions, photolysis, radiolysis

Citation

Grodkowski, J. and Neta, P. (2001), Copper-Catalyzed Radiolytic Reduction of CO₂ to CO in Aqueous Solutions, Journal of Physical Chemistry B (Accessed May 7, 2024)