The Promoting Effects of Various Alkali Metal Carbonates on the Reduction of Carbon Dioxide with Carbon

Abstract

The promoting effects of alkali metal carbonates, i. e. Li2CO₃, Na2CO₃, K2CO₃, Rb2CO₃ and Cs2CO₃, on the reduction of carbon dioxide with carbon were investigated. The activity for the production of carbon monoxide was proportional to the amount of oxygen taken-up on the surface during the reaction, irrespective of the sort of alkali metal. From the measurements of carbon dioxide adsorption onto these doped carbons at lower temperatures, of thermal desorption of carbon carrying potassium carbonate labeled with carbon-13, and of X-ray photoelectron spectroscopy; the following mechanism was proposed;
M₂CO₃ =M₂O + CO₂
M₂O + C =2M + CO
2M + CO₂ =M₂O + CO
where M refers to alkali metals. The overall reaction (C+CO₂=2CO) proceeds through the redox cycle of alkali metal oxide formed by the decomposition of carbonate.