H2 production based on a ternary mixture of commercial CuO-NiO-TiO2 in a solar pilot plant

Abstract

Glycerol is a by-product in biodiesel production (in the range of g·L−1), so its photoreforming by photocatalysis is a way of valorising it. TiO2 in photocatalysis has been widely studied, although its efficiency is limited by the high energy band gap, and the electron-hole recombination. Its combination with different semiconductors should improve charge separation, extending also the absorption from UV to visible light. Cu and Ni oxides are two of the most efficient low-cost transition metal oxide catalysts. Experiments were carried out in a 25 L pilot plant connected to a compound parabolic solar collector. Different combinations of the three semiconductors, based on the concentration of each metal on TiO2 (Me, 5%, 7.2% and 10%) were evaluated. Evonik P25-TiO2, CuO and NiO were combined by mechanical mixing. Hydrogen was quantified by a micro gas chromatograph, and copper and nickel leaching by ICP-MS. The best hydrogen production (0.060 mMol kJ−1) was attained with a proportion of 10:1 of TiO2:MeO, that corresponds to a total metal concentration of 7.2 wt%, being Cu and Ni in the same proportion. Metal content in solution increased as the reaction progressed, but Ni lixiviation of <0.012 mg L−1 was not significant. Significant Cu leaching (>1 mg L−1) was observed. This article presents novel results, in a solar pilot plant, for determining which ternary mixture can give better results, as well as metal leaching into water. Handling relevant volume of water in anoxic conditions can help to understand the application of this technology for the production of hydrogen.