Photocatalytic Steam Reforming of Methane over Sodium Tantalate

Abstract

Photocatalytic steam reforming of methane (CH 4 + 2H 2 O f 4H 2 + CO 2 ) was examined over modified and unmodified sodium tantalate photocatalysts around room temperature. The activity of the photocatalysts was much influenced by metal cation doped into the bulk of NaTaO 3 , the crystallites size of NaTaO 3 , and metal nanoparticles loaded on the surface. The highest activity was obtained over the NaTaO 3 doped with La 3+ , where a moderate amount of La 3+ should substitute for Na + without distorting the crystal structure of NaTaO 3 . The large crystallites size was a more important factor than the high surface area for higher photocatalytic activity of NaTaO 3 :La. These factors such as doping and large crystallites should increase the density and the mobility of the photoexcited carriers to improve the intrinsic photocatalytic activity. A moderate amount of Pt nanoparticles loaded on NaTaO 3 :La most enhanced the activity among the examined metal particles, which would contribute to not only separation of excited electrons from holes and the successive hydrogen production but also methane activation during reaction with water or holes. The heat treatment after the addition of Pt, which probably formed the practical metal-semiconductor junction, was required for a high and stable photocatalytic activity. The best photocatalyst, Pt/NaTaO 3 :La(2%), exhibited more than two times higher activity than Pt/TiO 2 did. The photocatalytic reaction lasted for a long time without deactivation. The effect of reaction conditions such as reaction temperature, feed gas composition, and light intensity on the catalytic performance was systematically optimized, and the highest H 2 production rate reached 4.5 µmol min -1 (270 µmol h -1 ), corresponding to 0.6% methane conversion and 11% water conversion, which exceeded the equilibrium conversion. The apparent quantum yield in the range of 240-270 nm for the hydrogen production was estimated to be 30% when the irradiation light intensity was 2 mW cm -2 , which was higher than that of the photocatalytic water-splitting system employing NiO/NaTaO 3 :La.

Hydrogen Production by Photoreforming of Renewable Substrates

“…Furthermore, gas phase applications for H 2 photocatalytic production are much more limited than liquid phase examples. A detailed investigation on methane photo-steam reforming has been proposed by Shimura et al [232]. Of course the interest would be the application with biogas.…”

CO2reforming of methane over highly active La-promoted Ni supported on SBA-15 catalysts: mechanism and kinetic modelling

“…23 In addition, modification with La can also effectively minimize sintering and improve thermal resistance at high temperatures. 32,33 However, most of the studies conducted for Ni/SBA-15 are carried out at low gas hourly space velocities (GHSVs) of less than 40 000 mL g cat −1 h −1 . 31 Moreover, the fascinating optical properties of lanthana have led to its utilization in the field of semiconductor photocatalysis as dopants.…”

Leaf-architectured 3D Hierarchical Artificial Photosynthetic System of Perovskite Titanates Towards CO2 Photoreduction Into Hydrocarbon Fuels

“…Loading Pt cocatalyst on STO could enhance the photocatalytic activity for water splitting47, but surprisingly not CO 2 reduction in STO, probably because although Pt functions as an efficient cocatalyst for H 2 evolution, it also catalyzes the reverse reaction of water formation from H 2 and O 2 . Furthermore, loading with Pt could significantly promote the so-called process of PSRM (Photocatalytic Steam Reforming of Methane)48. When Au, Ag and Cu cocatalysts (Supplementary Fig.…”