Decomposition Of Co₂ to Carbon by H₂-Activated Ni(II)- and Co(II)-Bearing Ferrites At 300°C

Abstract

The reactivity of the H₂-activated Ni(II)- and Co(II)-bearing ferrites with different levels of metal substitution have been studied for CO₂ → C decomposition in comparison with that of the H₂-activated magnetite. Ni²⁺ and Co²⁺ have been substituted for Fe²⁺ or Fe³⁺ in magnetite with the spinel-type structure up to 14 % and 26 % of the mole ratio of Ni₂₊ and Co^{2 +} to the total Fe content respectively. The reactivity of the Ni(II)- and Co(II)-bearing ferrite increased with the level of metal substitution. Especially, the Ni(II) substitution significantly facilitated the CO₂ → C decomposition in a batch system. The rates of H₂-activation (reduction) and CO₂-decomposition (oxidation) for N(II)-bearing ferrite were studied by a thermogravimeteric analysis. The rates of both H₂-activation and CO₂-decomposition were much improved in the Ni(II)-bearing ferrite with the Ni(II)/Fetoul mole ratio of 14%. It is considered that the reduced Ni(II) ions which were formed on the surface of the ferrite is very active to facilitate both dissociation reactions of 1) H₂ → 2 H_ads and 2) CO₂→ C_ads + 2O_ads,. From the change in the lattice constant of the Ni(II)-bearing ferrite during the H₂-activation and CO₂-decomposition, the oxygens in CO₂ were considered to be incorporated into the oxygen deficient spinel lattice of the oxygen deficient Ni(II)-bearing ferrite which had been formed by the H₂-activation.