Photocatalytic decomposition of acetaldehyde over TiO₂/SiO₂ catalyst

To establish a promising method for the purification of air containing volatile organic compounds, photocatalytic decompositions of gaseous acetaldehyde over TiO₂ deposited on porous silica (TiO₂/SiO₂ catalyst) and over a platinized TiO₂/SiO₂ catalyst (Pt-TiO₂/SiO₂ catalyst) have been investigated including the capture of intermediates on the catalyst surface and regeneration of the deactivated catalyst by heating. Results of kinetic analysis show that these photocatalytic decompositions obey Langmuir-Hinshelwood kinetics. A comparison between the amounts of acetaldehyde decomposed and CO₂ produced reveals that about 10 % of acetaldehyde is missing. From the observation of the photocatalyst surface before and after the reaction by FT-IR spectroscopy, we conclude that this is due to the adsorption of intermediates such as formic acid and acetic acid on the porous catalyst as well as deposition of coke-like substances. When the Pt-TiO₂/SiO₂ catalyst is heated to a temperature above 473 K, these substances can be removed and discharged as CO₂. A series of results obtained in the present work suggests that the use of a Pt-TiO₂/SiO₂ catalyst will enable us to construct a multifunctional reaction process for air purification, in which volatile organic compunds are photocatalytically decomposed. The harmful intermediates formed during the reaction are partly adsorbed on the porous catalyst, remain in the reactor system, and together with deposited coke-like substances are converted into CO₂ by heat treatment of the catalyst. The catalyst is thus regenerated.