Performance and Mechanism of Photocatalytic Toluene Degradation and Catalyst Regeneration by Thermal/UV Treatment.

This work presents a new strategy for industrial flue gas purification with TiO2-based photocatalysis technology, which could be achieved by a novel dual-stage circulating photocatalytic reactor. A lab-scale fixed bed reactor is utilized to investigate the performance of photocatalytic toluene degradation and inactive catalyst regeneration by thermal/UV treatment. The relationships between operational conditions and toluene oxidation are surveyed and discussed in detail. The results show that the intermediates could be further removed and decomposed by introducing UV radiation, compared with heat treatment alone. To reveal the photocatalytic mechanism and identify the accumulated intermediates over anatase TiO2, the adsorbed toluene and aromatic intermediates are identified by XPS, in situ DRIFTS, and on-line MS. The aromatic ring and other covalent bonds (C═O, C-O, and O-H) are detected during photocatalytic oxidation. The reaction pathway involving hydrogen abstraction is referred as the dominant pathway for toluene degradation, and ring opening via ·OH radicals is crucial to make aromatic intermediates change into CO2 and H2O. The results indicate that benzoic acid and benzaldehyde are the main accumulation because of their high reaction energy. A possible reaction mechanism is proposed for toluene oxidation, deactivation, and regeneration of catalysts, which has a significant value for guiding the practical applications.