Reduction of carbon dioxide into carbon by the active wustite and the mechanism of the reaction

Abstract

Normal wustite (Fe 0.94O) was prepared by rapidly decomposing ferrous oxalate in vacuum at 923 K. Normal wustite, which was kept in a He atmosphere at 573 K for 10 min, undergoes eutectoid decomposition into active wustite (Fe 0.98O) and stoichiometric magnetite. Compared with normal wustite, active wustite is more unstable and it is active for decomposing carbon dioxide. Carbon dioxide (1.013 × 10 5 Pa) was almost completely reduced into carbon by active wustite at 573 K, which was associated with the transformation of active wustite into stoichiometric magnetite. The oxygen in CO 2 is considered to be transferred to the surface of wustite in the form of O 2− ions and then these ions react with excess iron ions from the inside of the oxide to form the spinel structure. In order to maintain the electrical neutrality of the oxide, active wustite releases electrons, which will move to the surface and be donated to the carbon in CO 2; therefore the carbon is reduced. The reduction of CO 2 into carbon is undergone via two steps: CO 2 → CO → C, the former step, CO 2 → CO, is the control step of the reaction speed and CO is the intermediate of this reaction, because the speed of CO conversion is faster than that of CO 2 when CO was produced in the process of the reaction. During the reaction, the partial pressure of CO 2 decreased gradually with increasing reaction time and finally the reaction system became a vacuum. Elevating reaction temperature, the speed of CO 2 decomposition increased and the content of CO produced in the reaction process decreased.