Hydrogen evolution in the photocatalytic reaction between methane and water in the presence of CO2 on titanate and titania supported Rh and Au catalysts

The photocatalytic transformation of methane-water mixture over Rh and Au catalysts supported on protonated (H-form) titanate nanotube (TNT) was investigated. The role of the catalyst structure was analyzed using titania reference support. Furthermore the effect of carbon-dioxide addition was also investigated. The catalysts were characterized by high resolution transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). Photocatalytic tests were performed with a mercury-arc UV source illuminating a continuous flow quartz reactor which was attached to a mass spectrometer. The surface of the catalysts was analyzed by diffuse reflectance infrared spectroscopy during the photoreactions. The changes of the catalysts due to photocatalytic usage were investigated by XPS and temperature programmed reduction methods as well. Most of the methane was generally transformed to hydrogen and ethane, and a small amount of methanol was also formed. The carbon dioxide addition enhanced the rate of the photocatalytic transformation of methane on Rh/TNT with increasing the lifetime of the electron-hole pairs. Bigger gold particles with mainly plasmonic character were more active in the reactions due to the photo induced activation of the adsorbed water. Surface carbon deposits were identified on the catalysts after the photoreactions. More oxidized carbon formed on the Au-containing catalysts than on the ones with Rh.