Hydrogen Production from Methane and Water on Platinum Loaded Titanium Oxide Photocatalysts

Photocatalytic reaction of CH 4 gas with H 2 O vapor was examined over Pt/TiO 2 around room temperature (ca. 323 K) in a flow reactor. H 2 and CO 2 were the main products, and only trace amounts of C 2 H 6 and CO were also observed. After an induction period, the molar ratio of H 2 to CO 2 in the outlet gas became close to 4. Thus, the main reaction is suggested as the equation CH 4 + 2H 2 O(g) → 4H 2 + CO 2, which can be referred to as photocatalytic steam reforming of methane (photocatalytic SRM), where the photoenergy is converted to chemical potential of products (= 113 kJ mol -1 ). The reaction would be promoted by photoexcited electrons and holes, which were generated by band gap photoexcitation of the TiO 2 photocatalyst. The apparent quantum yield in the range 345−385 nm with high-intensity light (60 mW cm -2 ) was 0.6%, while the one in the range 240−270 nm with low-intensity light (2 mW cm -2 ) reached 2%. Highly active Pt/TiO 2 photocatalysts consisted of anatase phase TiO 2 having large surface area and enough loading amount (more than 0.1 wt %) of metallic Pt nanosized particles, which should be loaded by the photodeposition method, preferentially in the reaction condition. During the induction period, the photoirradiated side of the catalyst in the reaction cell turned pale brown, and the reaction was much accelerated. The colored surface substances accelerating the reaction rate, whose chemical formula can be described as [CH 2 O] n, were revealed as the reaction intermediates. The reaction mechanism was also investigated.