Intensification of gas-phase photoxidative dehydrogenation of ethanol to acetaldehyde by using phosphors as light carriers

摘要

In this work a significant improvement of VO_x/TiO2 photocatalytic activity in the selective partial oxidation of ethanol to acetaldehyde was achieved by the simultaneous irradiation with light emitting phosphorescent particles and UVA-LEDs as external light source. Photocatalytic tests were carried out in a gas-solid photocatalytic fiuidized bed reactor at high illumination efficiency, in which the bed is constituted by VOx/TiO2 photocatalyst at nominal V2O5 content of 5 wt% and suitable selected phosphors, diluted with glass spheres. In this way, phosphors were fiuidized together with the catalyst, excited by external UVA-LEDs, emitting their stored energy in close proximity to the catalyst. In the absence of phosphors the ethanol consumption rate initially grows linearly with initial alcohol concentration, then bends towards an asymptotic value for initial ethanol concentration higher than 0.5 vol%. By contrast, when phosphors are present, the ethanol consumption rate increased linearly in the overall range. In all cases acetaldehyde was the main product detected in gas phase with a selectivity of about 97%, ethylene and carbon dioxide the by-products. The results evidenced that the presence of phosphors allowed improved photon transfer, increasing the apparent quantum yield from 2 to 30% together with a high photoreactivity.