A step forwards in ethanol selective photo-oxidation

Abstract

This work focuses on the optimization of a photocatalyst formulation for the selective oxidation of ethanol to acetaldehyde. VO_x/TiO₂ catalysts at different vanadium loading were studied in a gas–solid photocatalytic fluidized bed reactor at high illumination efficiency, in which the bed is constituted by photocatalyst diluted with α-Al₂O₃ or silica gel. Photocatalytic tests showed the selective formation of acetaldehyde, with ethylene and carbon dioxide as by-products. Selectivity is influenced by the vanadium loading. For ethanol inlet concentration of 0.2 vol%, maximum conversion and acetaldehyde selectivity of 73% and 97%, respectively, were obtained at 100 °C on catalyst at nominal 5 wt% V₂O₅ content (53% of surface monolayer) mixed with α-Al₂O₃. Selective sites were related to surface polymeric vanadates possessing Ti–O–V and V–O–V functionalities while the photoactivity appeared correlated with the catalyst equivalent band gap energy. Increasing the ethanol inlet concentration to 1 vol% and diluting the catalyst with silica gel, total ethanol conversion with about 97% selectivity to acetaldehyde was achieved with a photoreactivity of 0.34 mol m_irradiated⁻³ s⁻¹. This is three times higher than reported for other photoreactors.