Preparation of sodium hexatitanate photocatalysts by a flux method for photocatalytic steam reforming of methane

Fine crystals of sodium hexatitanate (Na₂Ti₆O₁₃) were prepared by a flux method for photocatalytic steam reforming of methane (PSRM) to produce hydrogen. The examined parameters for the preparation in this study were the solute concentration in the molten sodium chloride salt and the cooling rate from the molten mixture. As a reference, another sample was prepared by a solid state reaction method, which corresponds to the preparation without the sodium chloride flux. The prepared samples consisted of hexagonal rod-like microcrystals of monoclinic structure with various morphology, particle size, crystallite size, aspect ratio, and specific surface area. The solute concentration affected the length and the aspect ratio of the rod-like structure although the cooling rate did not so much. The samples were loaded with 0.05 wt% of Rh cocatalyst nanoparticles, which was well dispersed oxide species on the surface. The Rh-loaded samples exhibited photocatalytic activity for hydrogen production in the PSRM. It was found that the photocatalytic production rate varied with the various structural parameters, especially correlated with the crystallite size of the rod-like Na₂Ti₆O₁₃ fine crystals

Platinum loaded sodium tantalate photocatalysts prepared by a flux method for photocatalytic steam reforming of methane

Lanthanum-doped sodium tantalate samples (NaTaO3:La) were prepared by a flux method using a sodium chloride flux with various parameters, such as presence or absence of the flux, solute concentration, hold temperature, and amount of lanthanum doping. SEM images showed cubic and rectangular shapes for the samples prepared by the flux method, somewhat rounded shape for the sample prepared in the absence of the flux, and large particles for the sample without lanthanum doping. Among the parameters, the lanthanum doping and solute concentration much influenced the crystallites size of the NaTaO3:La samples. Most of these NaTaO3:La samples loaded with platinum cocatalyst exhibited the photocatalytic activity in the photocatalytic steam reforming of methane around room temperature. Among them, the highest activity was obtained by the Pt/NaTaO3:La sample prepared by the flux method with moderate solute concentration, enough high hold temperature, and moderate amount of platinum and lanthanum doping. A positive correlation was found between the crystallite size and the photocatalytic activity. When we compared the catalysts having the same crystallite size, the sample prepared by the flux method showed higher photocatalytic activity than the catalyst prepared without the flux. It is suggested that the difference in the shape of particle would be important factor for the photocatalytic activity