Reaction Steps in Heterogeneous Photocatalytic Oxidation of Toluene in Gas Phase—A Review

Authors

Yerzhigit Tulebekov, Al-Farabi Kazakh National University
Zhandos Orazov, Al-Farabi Kazakh National University
Bagdat Satybaldiyev, Al-Farabi Kazakh National University, LLP «EcoRadSM»
Daniel D. Snow, University of Nebraska at LincolnFollow
Raphaël Schneider, Université de Lorraine
Bolat Uralbekov, Al-Farabi Kazakh National University, LLP «EcoRadSM»

Date of this Version

9-6-2023

Citation

Tulebekov, Y.; Orazov, Z.; Satybaldiyev, B.; Snow, D.D.; Schneider, R.; Uralbekov, B. Reaction Steps in Heterogeneous Photocatalytic Oxidation of Toluene in Gas Phase—A Review. Molecules 2023, 28, 6451. https://doi.org/ 10.3390/molecules28186451

Comments

Open access.

Abstract

A review of the current literature shows there is no clear consensus regarding the reaction mechanisms of air-borne aromatic compounds such as toluene by photocatalytic oxidation. Potential oxidation reactions over TiO₂ or TiO₂-based catalysts under ultraviolet and visible (UV/VIS) illumination are most commonly considered for removal of these pollutants. Along the pathways from a model pollutant, toluene, to final mineralization products (CO₂ and H₂O), the formation of several intermediates via specific reactions include parallel oxidation reactions and formation of less-reactive intermediates on the TiO₂ surface. The latter may occupy active adsorption sites and causes drastic catalyst deactivation in some cases. Major hazardous gas-phase intermediates are benzene and formaldehyde, classified by the International Agency for Research on Cancer (IARC) as Group 1 carcinogenic compounds. Adsorbed intermediates leading to catalyst deactivation are benzaldehyde, benzoic acid, and cresols. The three most typical pathways of toluene photocatalytic oxidation are reviewed: methyl group oxidation, aromatic ring oxidation, and aromatic ring opening.