Steam reforming of methane by titanium oxide photocatalysts with hollow spheres

Steam reforming of methane (SRM) is one of the most useful techniques for methane (CH4) conversion because of the large hydrogen yield per CH4 molecule. However, this process is not commercially viable due to the high reaction temperature and associated energy costs. To decrease the SRM reaction temperature, the introduction of photochemical energy has been proposed; however, the charge recombination of photo-generated carriers must be suppressed to achieve higher activity. Here, TiO2 photocatalysts with a hollow sphere structure are synthesized and loaded with spatially separated co-catalysts to achieve high charge separation in an attempt to improve SRM efficiency. The highest SRM activity is observed for hollow-sphere structured TiO2 with Pt and Rh2O3 co-catalysts selectively deposited on the inner and outer TiO2 surfaces, respectively. In situ electron spin resonance and photo-luminescence measurements clearly demonstrate that photo-excited electrons and holes are trapped at Pt and Rh2O3 sites, respectively, of Rh/hollow TiO2/Pt, resulting in efficient charge separation and increased SRM activity. Taken together, these findings support our hypothesis that the spatial separation and heterogeneous loading of co-catalysts is a promising design strategy for photocatalytic methane conversion reactions.