Adsorption and photo-oxidation of acetaldehyde on TiO2 and sulfate-modified TiO2: Studies by in situ FTIR spectroscopy and micro-kinetic modeling

Adsorption and photocatalytic oxidation of acetaldehyde on TiO2 and SO4–TiO2. Acetaldehyde condensation to crotonaldehyde occurs on TiO2, but not on SO4–TiO2. Photo-oxidation of intermediates formate is the rate-determining step on TiO2, while it is acetaldehyde photo-oxidation on SO4–TiO2. •Sulfate-modified TiO2 (SO4TiO2) films have been fabricated by photo-fixation of SO2 on nanocrystalline anatase TiO2.•Elementary steps for acetaldehyde photo-oxidation have been quantified by in situ FTIR spectroscopy.•Acetaldehyde condensation to crotonaldehyde occurs on TiO2, but is suppressed on SO4TiO2.•Photo-oxidation of formate is the rate-determining step on TiO2, while it is acetaldehyde photo-oxidation on SO4TiO2.•The selectivity of the photo-oxidation is changed on SO4TiO2, leading to weaker bonding of intermediates, and sustained reactivity. Adsorption and photocatalytic oxidation of acetaldehyde have been investigated on TiO2 and sulfate-modified TiO2 films (denoted SO4TiO2). In situ Fourier transform infrared spectroscopy was used to study surface reactions as a function of time and number of experimental cycles. Spectral analysis and micro-kinetic modeling show that crotonaldehyde formation occurs spontaneously on TiO2 but is impeded on SO4TiO2, where instead acetaldehyde desorption is significant. Photo-oxidation yields significant amounts of formate on TiO2 and was identified as the rate-determining step and associated with site blocking. Significantly smaller amounts of formate were observed on SO4TiO2, which is due to the acidity of this surface resulting in weaker bonding of aldehyde and carboxylate intermediate species. Our results are of considerable interest for applications to photocatalytic air purification and to surfaces with controlled wettability.