Photocatalytic oxidation of n-butanol under fluorescent visible light lamp over commercial TiO2 (Hombicat UV100 and Degussa P25)

Photocatalytic oxidation (PCO) of volatile organic compounds (VOC) over TiO2, exploiting visible light of common fluorescent lamps represents an attractive means of indoor air purification. This work compares activity and its variation with calcination of two commercial TiO2, Hombicat UV100 and Degussa P25, in a complete PCO of n-butanol serving as a convenient representative VOC. The PCO of n-butanol was carried out in a flow through reactor under a relatively long residence time using mostly fluorescent visible (white) light (FWL)-lamp for illumination. Fluorescent black light (UV) (FBL)-lamp was used only for comparison. Under FBL-lamp, 580 ppm n-butanol is completely mineralized over both catalysts. Under FWL-lamp the reaction is considerably slower and Degussa P25 appears more active than Hombicat UV100. For 580 ppm, steady state conversions of less than 95% are attained, but at 145 ppm, a complete mineralization is achieved even over Hombicat UV100. Butanal, propanal and ethanal were identified as the main gaseous intermediate products. In addition, a parallel formation of crotonaldehyde, product of aldolization, was detected. The appearance and concentration of crotonaldehyde depended on PCO conditions, particularly on the characteristics of TiO2. Thermal treatment of TiO2 at ≥623 K has a negative effect on the activity in PCO of both catalysts. Apparently, the calcination causes modification of the surface available active sites that is in part reflected by diminution of specific surface area. The effect of reactor residence time, of inlet concentration and of the relative light intensity on the efficiency of the process was also evaluated.