PURPOSE: To nearly completely decompose NOx by bringing NOx-contg. gas into a catalytic reaction with activated magnetite obtd. by causing oxygen lattice defects in the solid crystals of magnetite granules.

CONSTITUTION: Part of oxygen is removed from the crystal lattice of Fe3O4 granules by allowing the Fe3O4 to react with hydrogen at about 300°C or setting the Fe3O4 in vacuum to synthesize activated magnetite. when NOx-contg. gas is brought into contact with the activated magnetite, this magnetite draws O2- ions into the O2--deficient lattice and further draws O2- ions by coupling into a reaction by which Fe2+ ions convert to Fe3+ ions, accordingly the NOx can be nearly completely decomposed.