Gas-phase ethanol photocatalytic degradation study with TiO2 doped with Fe, Pd and Cu

Abstract

Ethanol degradation by TiO2 and TiO2 doped with Fe, Pd and Cu has undergone FTIR spectroscopic study. Ethanol interaction with bare-TiO2 and Fe-TiO2 yields the formation of ethoxides on the catalyst surface that can readily be oxidised to acetates by radicals O2− and OH. Conversely, ethanol interaction with Pd-TiO2 and Cu-TiO2 generates an intermediate species between ethanol and ethyleneglycol. Acetate-producing oxidation of these latter species is inhibited because electrons that form radicals O2− are captured by the respective metallic oxides. In these catalysts a degradation mechanism based on ethanol reaction with photogenerated holes is proposed. Also, different surfacial OH distributions determine ethanol–catalyst interactions. Furthermore, ethanol degradation has been studied in a gaseous continuous flow system. Exhaust gases have been analysed by means of GC and FTIR. These experiments demonstrate that bare-TiO2 and Fe-TiO2 degrade ethanol to provide only acetaldehyde and their catalytic activity progressively decays over time. On the contrary, Pd-TiO2 and Cu-TiO2 have produced ethyleneglycol in addition to acetaldehyde. No deactivation of these catalysts was observed during the experimental time period (6 h). During the gas-phase ethanol photocatalytic degradation in a continuos flow system, bare-TiO2 and Fe-TiO2 are deactivated in opposition to what was observed for Pd-TiO2 and Cu-TiO2. Pd and Cu oxide deposits can be capturing the photogenerated electrons, thus avoiding the formation of O2− radicals that generate acetates.