Simultaneous Photocatalytic Abatement of NO and SO₂: Influence of the TiO₂ Nature and Mechanistic Insights

Title:Simultaneous Photocatalytic Abatement of NO and SO₂: Influence of the TiO₂ Nature and Mechanistic Insights

Volume: 2

Author(s): María D. Hernández-Alonso, Silvia Suárez , Fernando Fresno, Juan M. Coronado*Benigno Sánchez*

Affiliation:

• Instituto de Catalisis y Petroleoquimica, CSIC, Marie Curie, 2, Cantoblanco, 28049 Madrid,Spain

• FOTOAIR-Ciemat, Unit of Analysis and of Photocatalytic Treatment of Pollutants in Air. Renewable Energies Division CIEMAT. Avenida Complutense 40, Bldg. 42. 28040 Madrid,Spain

Keywords: Photocatalysis, air treatment, NO_x, nitrates, NO₂, SO₂, TiO₂, hydrothermal synthesis, DRIFT.

Abstract:

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 NO_x 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 NO_x 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 NO_x 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 UV irradiation.

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 formed.

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.

Cite this article as:

Hernández-Alonso D. María , Suárez Silvia , Fresno Fernando, Coronado M. Juan *, Sánchez Benigno *, Simultaneous Photocatalytic Abatement of NO and SO₂: Influence of the TiO₂ Nature and Mechanistic Insights, Journal of Photocatalysis 2021; 2 (2) . https://dx.doi.org/10.2174/2665976X02666210303124330