X-ray diffraction and electron magnetic resonance studies of M/Fe/Al₂O₃ (M=Ni, Mo and Pd) catalysts for CH₄ to H₂ conversion

Efficient production of hydrogen (H₂) from methane (CH₄) at 700 °C has been recently demonstrated using the reduced catalysts 0.5% M/4.5% Fe/Al₂O₃ (M=Ni, Mo, Pd). In this work, X-ray diffraction (XRD) at 300 K and electron magnetic resonance (EMR) spectroscopy at 5 and 300 K were used to determine the nature of the different phases present in these materials before and after the reaction with CH₄ at 700 °C to produce H₂. It is observed that before the reaction, catalysts reduced at 700 °C contain γ-Al₂O₃, elemental Fe, iron oxides and Fe³⁺ substituting for Al³⁺ in Al₂O₃, and that the presence of Ni, Mo and Pd promotes the reduction of iron oxides to Fe. In the post reaction catalysts, the amount of Fe is considerably lowered and the presence of Fe₃C and graphitic nanotubes is observed. However, there are no significant changes in the concentrations of Fe³⁺/Al₂O₃ and the iron oxides. The materials aspects of these results for the production of H₂ from CH₄ at 700 °C are discussed.