The Cation-deficient magnetite (Fe3+δO4, 0.2>δ>0) was synthesized by the air oxidation of Fe(OH)2 suspensions at 358K. The cation-excess magnetite (Fe3+δO4, 0.2>δ>0) was obtained by flowing H2 gas through cation-deficient magnetite at 563K, the stability of the magnetite is examined at various temperpatures and under atomspheres. Reactivity of Fe3+δO4 (0.2>δ>0) to reduce CO2 gas into carbon was studied at 358K. The results confirm that CO2 was nearly 100% decomposed into carbon, the oxygen in the CO2 is transferred, in the form of O^2^-, to the cation excess magnetite. The bigger the cation-excess degree of magnetite, the higher the decomposition activation of CO2 is, the more the amount of decomposited CO2.

Key words: CARBON DIOXIDE, MAGNETITE, DECOMPOSITION, IRON OXIDE, FERROUS HYDROXIDE