Toluene degradation over Mn-TiO2/CeO2 composite catalyst under vacuum ultraviolet (VUV) irradiation

Abstract

Volatile organic compounds (VOCs) are attracting more and more attention among all the air pollutants. Photocatalytic oxidation under vacuum ultraviolet (VUV) irradiation presents a novel and promising process for VOC degradation while also generating ozone as a byproduct. To improve the degradation efficiency of VOCs and remove the residual ozone Mn-TiO2/mesoporous CeO2 composite catalysts were developed and used as a catalyst in a VUV-PCO system for toluene degradation. Characterizations including SEM, TEM, BET, XRD, XPS, Raman and H2-TPR, were conducted to examine the physical and chemical features of the synthetic samples. Results of a toluene degradation test showed that the Mn-TiO2/CeO2 catalyst had superior activity in removing toluene and ozone to Mn-TiO2 and pure CeO2. The toluene removal efficiencies of the catalysts with a different molar ratio of Ti/Ce were found to be in the order of Mn-TiO2/CeO2 (1:1) > Mn-TiO2/CeO2 (1:2) > Mn-TiO2/CeO2 (2:1). The mineralization rate increased in the order of Mn-TiO2/CeO2 (1:1) > Mn-TiO2/CeO2 (2:1) ≈ Mn-TiO2 > Mn-TiO2/CeO2 (1:2) > CeO2 > VUV photolysis. High ozone removal rates of over 99.9% were obtained for all the doped samples with Mn, resulting in a residual ozone lower than 0.12 ppm. With the use of the scavenger tert-butanol (TBA) and the electron spin resonance (ESR) test, hydroxyl radicals (OH) were found to play a significant role in toluene oxidation in the VUV-PCO process and ozone is also involved in the formation of OH.