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

Abstract

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.