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

::2CO $ightleftharpoons$ CO₂ + C

According to the Ellingham diagram, the formation enthalpy of CO₂ by oxidation of carbon is constant and indifferent of the temperature, while the formation enthalpy of CO is a decreasing line. 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 product, as predicted by the Le Chatelier's Principle.

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 defines the equilibrium formation enthalpy on function of 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.