Decomposition of CO₂ to carbon by H₂-reduced Ni(II)- and Co(II)-bearing ferrites at 300 °C

Abstract

Ni(II)- and Co(II)-bearing ferrites with different levels of metal substitution have been studied for CO₂ decomposition. Ni²⁺ and Co²⁺ have been substituted for Fe²⁺ or Fe³⁺ in magnetite with the spinel type of crystal structure up to 14% and 26% for the mole ratio of Ni²⁺ and Co²⁺ to the total Fe contents, respectively. The metal substitution was corroborated by Mössbauer spectroscopy and XRD studies. They were activated in a flow of H₂ gas to form oxygen-deficient ferrites with the spinel structure retained. The oxygen-deficient M(II)-bearing ferrites have been found to show high reactivity toward CO₂ decomposition to carbon at 300 °C. The reactivity increased with the level of metal substitution and activation. The oxygens of CO₂ were incorporated into the spinel structure and carbon was deposited on the surface of the ferrites. The deposited carbon was visible on dissolution of the ferrites used. The rate of decomposition on H₂-activated Ni(II)-bearing ferrite with the mole ratio of 14% was 30 times as high as that of H₂-activated magnetite.