Boudouard reaction

The Boudouard reaction is the redox reaction of a chemical equilibrium mixture of carbon monoxide and carbon dioxide at a given temperature. It is the disproportionation of carbon monoxide into carbon dioxide and graphite or its reverse:^[1]

2CO CO₂ + C

While formation enthalpy of CO₂ is higher than that of CO, the formation entropy is much lower. Consequently, according to the Ellingham diagram, the overall free energy change of formation of CO₂ by oxidation of carbon is almost constant and indifferent of the temperature, while the free energy change of formation of CO is a decreasing line. These two lines meet at 700℃, so the Boudouard reaction implies that on lower temperatures the equilibrium is on the exothermic carbon dioxide side and on higher temperatures the endothermic formation of carbon monoxide is the dominant reaction.
For instance, in the high temperature reducing environment of a smokestack, carbon monoxide is the stable product. When the carbon monoxide reaches the top of the smokestack, and the cooler air, the Boudouard Reaction takes place; the carbon monoxide is oxidized into carbon dioxide, and the graphite precipitates (reduces) as soot. The Ellingham diagram is a plot of the Gibbs free energy change for a reaction (ΔG), versus temperature.
In industrial catalysis, this is not just an eyesore; the coking can cause irreversible damage to catalysts and catalyst beds. This reaction also takes place in blast furnaces where carbon monoxide is used as the reductive agent on purifying metallic iron from its oxides in ore.



The reaction is named after the French chemist, Octave Leopold Boudouard (1872—1923) who investigated this equilibrium in 1905.^[3]