Photocatalytic production of hydrogen from methanol and saccharides using carbon nanotube-TiO2 catalysts

• CNT-TiO2 composites were produced by hydration–dehydration and by one-pot oxidation.
• One-pot oxidation synthesis leads to a better dispersion of TiO2 in composites.
• TiO2 and CNT-TiO2 were loaded with Pt, Ir, Au and Pd by incipient wetness.
• Cocatalyst nature and reduction temperature influence H2 production from methanol.
• H2 yield from saccharides depends on structure, H:C ratio and availability of α-H.

Carbon nanotube-titanium dioxide composite materials were produced by two routes: hydration–dehydration and one-pot oxidation. Au, Pt, Ir and Pd were loaded on TiO2-based materials by an incipient wetness method. The resulting materials were calcined and afterwards reduced at two distinct temperatures, 473 and 673 K. Characterization was carried out by temperature programmed desorption, infrared and UV–Vis spectroscopy, N2 adsorption, SEM and TEM. Compared with reference TiO2, composite catalysts presented increased activity for photocatalytic production of H2 from methanol solutions. The highest activity was obtained for the Pt-loaded composite produced by the one-pot synthesis method, with 485 μmol of H2 being generated after two hours of irradiation, contrasting with 205 μmol of H2 obtained using Pt/TiO2. This synergic effect was discussed in terms of the action of carbon nanotubes as dispersing media for TiO2 particles as well as their action as photosensitizers. The relative efficiency of the catalysts was related to the work function of each metal and the sizes of the metal nanoparticles. H2 generation from photocatalytic reforming of saccharides, namely arabinose, glucose, fructose and cellobiose was performed using TiO2 and CNT-TiO2 based catalysts. The relative efficiency of H2 production from these biomass-derived compounds has been discussed based on their structural arrangement, H:C ratio and availability of α-hydrogens.

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