Photocatalytic hydrogen production from aqueous methanol solution using Pt nanocatalysts supported on mesoporous TiO2 hollow shells

Abstract

Mesoporous TiO 2 hollow shells were synthesized by a conventional templating method which combines sol-gel coating and selective etching of the silica cores. Pt nanocatalysts were supported on these mesoporous TiO 2 hollow shells varying the metal loading: 0, 1, 3, 5 and 7 % at calcination temperatures of 500 or 900°C. The samples were characterized by transmission electron microscopy, X-ray diffraction, UV-Vis diffuse reflectance spectroscopy, and nitrogen physisorption. The mesostructures were observed by TEM and HRTEM to be smaller than 300 nm and the TiO 2 shells had an average wall thickness of 40 nm. X-ray diffraction spectra revealed a pure anatase phase in samples calcined at 900°C, whereas those calcined at 500°C were amorphous. Under white light (UV and Visible) illumination, photocatalytic hydrogen production was measured from the samples suspended in an aqueous solution of methanol and compared to TiO 2 (P25, Degussa) used as a reference. The highest hydrogen yields were achieved with the crystalline TiO 2 hollow shells annealed at 900°C containing 1 or 7 wt% Pt. The amorphous samples were observed to be inactive, at all metal loadings. Graphical Abstract

Introducing catalysis in photocatalysis: What can be understood from surface science studies of alcohol photoreforming on TiO2

“…In latter case, the photoelectron generated by the illumination may reduce the surface proton similar as in the electrochemical picture as proposed by Zaera and coworkers [136][137][138][139]. However, this reaction can be discarded under UHV conditions, because the reaction of tert-butanol of bare titania [67], its photorefoming of the platinum-loaded crystal [24] and the photooxidation of acetone [140][141][142][143] clearly demonstrates that a second neutral species (a methyl radical) is created under illumination.…”

Toward a Comprehensive Understanding of Photocatalysis: What Systematic Studies and Alcohol Surface Chemistry on TiO2(110) Have to Offer for Future Developments

“…The reaction therefore never relies on fully ionic species. This clearly separates the mechanism from reaction schemes with a formation of surface hydroxyl by photogenerated electrons on the semiconductor surface as in the works of Zaera and co-workers. − Still, both reactions share the common characteristics of a thermal recombination of hydroxyls on the metal particles as the last step of H 2 formation. The conversion of reactants from the gas phase in the absence of liquid films on the semiconductor, as under the conditions of our work, rules out the presence of solvated ions and supports our mechanistic picture.…”