CuOx-TiO2 Photocatalysts for H2 Production from Ethanol and Glycerol Solutions

Hydrogen production by photocatalytic reforming of aqueous solutions of ethanol and glycerol was studied with the use of impregnated and embedded CuOx/TiO2 photocatalysts. Embedded CuOx@TiO2 was prepared by a water-in-oil microemulsion method, which consists in the formation of Cu nanoparticles in the microemulsion followed by controlled hydrolysis and condensation of tetraisopropyl orthotitanate with the aim of covering the protected metal particles with a surrounding layer of porous titanium oxyhydroxide. Mild calcination leads to the complete removal of the organic residues, the crystallization of TiO2, and an unavoidable oxidation of copper. Two reference samples were prepared by classical wet impregnation of preformed TiO2 with different ratios of anatase, rutile, and brookite polymorphs. The two supports were prepared by sol-gel (TiO2-SG) and microemulsion (TiO2-ME) methods. Superior performances have been observed for the embedded system, which shows higher hydrogen production rates with respect to the impregnated systems using either ethanol or glycerol as sacrificial molecules. Deep structural characterization of the materials has been performed by coupling high resolution transmission electron microscopy (HRTEM), high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), X-ray absorption fine structure (XAFS), and electron paramagnetic resonance (EPR) techniques. Correlation between copper oxidation state and its dispersion and reactivity has been attempted. Finally, the stability of the CuOx/TiO2 catalysts was also studied with respect to carbonaceous deposits and copper leaching.