CO2 DECOMPOSITION WITH OXYGEN-DEFICIENT MN(II) FERRITE

An oxygen-deficient Mn(II) ferrite (Mn0.97Fe2.02O3.92) was synthesized and its reactivity to reduce CO2 gas into carbon was studied at 300-degrees-C. The oxygen-deficient Mn(II) ferrite was obtained by flowing H-2 gas through Mn(II) ferrite with a nearly stoichiometric composition of Mn0.97Fe2.02O4.00 at 300-degrees-C. The lattice constant of the oxygen-deficient Mn(II) ferrite (0.8505 nm) is larger than that of the Mn(II) ferrite with a nearly stoichiometric composition (0.8498 nm). The chemical composition of the Mn(II) ferrite changed from Mn0.97Fe2.02O4.00 to Mn0.97Fe2.02O3.92 during the H-2 reduction process, indicating that the oxygen is deficient in the spinel structure of the Mn(II) ferrite. This was confirmed by Mossbauer spectroscopy and X-ray diffractometry. The efficiency of CO2 decomposition into carbon at 300-degrees-C with the oxygen-deficient Mn(II) ferrite was much lower by about 10(5) than that of oxygen-deficient magnetite. This is considered to be due to the difference in electron conductivity between Mn(II) ferrite and magnetite, which determines the reductivity for CO2 into carbon by donation of an electron at the adsorption site.