Redox of titanium oxides by methane and water for application to cyclic syngas and hydrogen production systems

Characteristics of TiO₂ reduction by methane and re-oxidation by water were investigated at 1223 and 1273 K. The aim of this study was to evaluate the potential of TiO₂ as a stable support material for other oxides, such as CeO₂ and WO₃, which could be used for cyclic production of hydrogen and syngas by methane reforming and water splitting. TiO₂ was reduced successively to Ti₄O₇, Ti₃O₅, and Ti₂O₃. During the reduction, methane decomposition to hydrogen and solid carbon occurred slightly from the onset. When the extent of TiO₂ reduction (EOR) reached approximately 20%, methane decomposition to hydrogen and solid carbon started to occur significantly. Re-oxidation of the reduced titanium oxides by water splitting was not complete, at 30-80%, and the solid carbon was difficult to remove by water. During repeated cyclic operations, both the EOR and the re-oxidation percentage decreased gradually; one main reason for this is due to the deposited solid carbon. Therefore, TiO₂ possesses a great potential as a stable support for redox systems of CeO₂ and WO₃ that operate at lower temperatures and/or for shorter times.