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

Ga 2 O 3 photocatalysts showed a high and stable activity for the photocatalytic steam reforming of methane (PSRM; 2H 2 O(g) + CH 4 → 4H 2 + CO 2 ) around room temperature. The activity was much influenced by the cocatalyst and the crystal structure of Ga 2 O 3; the highest activity was obtained over Pt-loaded β-type Ga 2 O 3 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 Ga 2 O 3 was also effective to improve the photocatalytic activity; metal cations having both a smaller oxidation number than that of Ga 3+ and a similar ionic radius to that of Ga 3+, such as Mg 2+ and Zn 2+, were effective as the dopant into the bulk of β-Ga 2 O 3, while cations of the aluminum group such as In 3+ and Al 3+ were effective as the surface additives. When we compared the activity for the PSRM with those for the water decomposition (WD; H 2 O → H 2 + 1 / 2 O 2 ) and the methane decomposition (MD; CH 4 → x /2H 2 + CH 4− 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.