Background: TiO2 is currently being incorporated into several construction materials, such
as cement and asphalt because this photocatalyst can act as a passive system to reduce the concentration
of typical urban pollutants like NOx and SO2 under solar illumination.
Objective: In order to get further insights on the possible influence of the interaction between common
pollutants, the present work investigates the mechanism of NOx photo-oxidation in the presence of
SO2 traces over TiO2 samples of different textural and morphological characteristics.
Methods: The performance for the photo-oxidation of NOx and SO2 in a dry air stream over TiO2
samples, both commercial and lab-prepared by hydrothermal and thermal methods, was evaluated by
means of FTIR analyses of the gas phase. These materials were characterized by XRD, N2 adsorption
isotherms, and DR UV-vis spectroscopy. Mechanistic studies were performed by in situ DRIFT under
Results: Photocatalytic tests showed a very efficient removal of the two selected pollutants using most
of the TiO2 samples. In the case of SO2, elimination of these molecules is due not only to photocatalytic
oxidation but also to a significant extent, to adsorption. Although in shorter periods, no byproducts
are generated, following irradiation for several hours, the production of NO2 progressively
increases and reaches 100 % selectivity over some photocatalyst. In situ DRIFTS analyses show the
evolution of the surface composition and reveal the formation of the different types of surface nitrates
with different symmetry. Under these operating conditions, a minor amount of sulfates are also
Conclusion: The presence of a low concentration of SO2 does not appear to be detrimental for NO
removal. NO2 formation is delayed on the TiO2 samples with high specific surface area, which also
tend to be more active. The spectroscopic results confirm the involvement of surface hydroxyls in the
formation of adsorbed nitrate species.