Photocatalytic Activation of Water and Methane over Modified Gallium Oxide for Hydrogen Production

Ga2O3 photocatalysts showed a high and stable activity for the photocatalytic steam reforming of methane (PSRM; 2H(2)O(g) + CH4 -> 4H(2) + CO2) around room temperature. The activity was much influenced by the cocatalyst and the crystal structure of Ga2O3; the highest activity was obtained over Pt-loaded beta-type Ga2O3 with specific surface area of 10-20 m(2) g(-1). The addition of metal cations into the bulk and/or on the surface of Ga2O3 was also effective to improve the photocatalytic activity; metal cations having both a smaller oxidation number than that of Ga3+ and a similar ionic radius to that of Ga3+, such as Mg2+ and Zn2+, were effective as the dopant into the bulk of beta-Ga2O3, while cations of the aluminum group such as In3+ and Al3+ were effective as the surface additives. When we compared the activity for the PSRM with those for the water decomposition (WD; H2O -> H-2 + 1/2O(2)) and the methane decomposition (MD; CH4 -> x/2H(2) + CH4-x), it was revealed that the improvement of the bulk processes would mainly influence the water activation while that of the surface processes would affect the methane activation.