Synthesis of carbon-iron(II) oxide layer on the surface of magnetite and its reactivity with H₂O for hydrogen generation

Abstract

Synthesis of a carbon-iron(II) oxide layer on the surface of magnetite and its reactivity with H₂O for hydrogen generation reaction have been studied. X-ray diffractometry and chemical analysis showed that the carbon-bearing magnetite synthesized by the carbon-deposition reaction from CO₂ gas with the hydrogen-reduced magnetite, was magnetite with a carbon-iron(II) oxide layer (CIO layer-M; M is stoichiometric magnetite) represented by (Fe₃O₄)_1−δ (Fe₃O₃)_δC_τ. The TG-MS spectra also showed the evidence for the formation of the CIO layer on the bulk stoichiometric magnetite. Some amorphous phase was formed in the CIO layer during the activation step (in vacuo at 300 °C for 30 min). This amorphous phase reacted with H₂O and evolved H₂ gas at 350 °C. This H₂ generation reaction resulted in the oxidation of the CIO layer into γ-Fe₂O₃ component and the release of a part of carbon in the CIO layer as CO₂. The X-ray diffractometry and Mössbauer spectroscopy indicated that the solid solution of Fe₃O₄-γ-Fe₂O₃ was formed in the solid phase after the H₂ generation reaction. This shows the cation movement in the B site of the bulk magnetite of the activated CIO layer-M during the H₂ generation reaction. The TG-MS spectra also supported the above estimation.