Photocatalytic oxidation of benzene, toluene, ethylbenzene and m-xylene in the gas-phase over TiO2-based catalysts

In the present work, the photocatalytic oxidation of benzene, toluene, ethylbenzene and m-xylene (BTEX) in the gas phase over various UV-irradiated TiO2-based catalysts was studied. Specifically, five catalysts were tested: four based on P25 from Degussa adding 0.25% (w/w) Pt, Fe or Ce (P25, P25/Pt, P25/Fe, P25/Ce) and one prepared according to the isopropoxide method. Inlet BTEX concentrations ranged in 0.5–21 ppmv, whereas oxygen concentration was fixed (21%, v/v) at all experiments and the residence time was adjusted to 11.5 s. Ce addition to P25 catalyst led to the highest photocatalytic oxidation rates for benzene and ethylbenzene, whereas P25 proved to be the most active catalyst on toluene photo-oxidation. Regarding m-xylene, the choice of the most effective catalyst depended on m-xylene reactor concentration. Taking all experimental results into account, P25/Ce was the most effective catalyst due to its superiority in the case of benzene and ethylbenzene and its comparable performance to the base catalyst for toluene and m-xylene photocatalytic oxidation. In general, all P25 based catalysts were more active than the isopropoxide catalyst. All conversions showed great dependence on the inlet concentration of the target compound. Water addition to the reactor during ethylbenzene photo-oxidation enhanced the rates achieved for all catalysts tested. It has to be noted that the differences in the reaction rates achieved from catalyst to catalyst decreased with water vapours addition to the reactor. Finally, a Langmuir–Hinshelwood kinetic model has been applied to the experimental data obtained. The kinetic data obtained confirmed the strong beneficial effect of Ce addition to P25 catalyst on benzene and ethylbenzene photocatalytic oxidation.

► Ce addition to TiO2 enhanced photo-oxidation rates of benzene and ethylbenzene.
► BTEX conversions showed great dependence on the target compounds’ concentration.
► Water enhanced photo-oxidation rates and decreased the impact of catalyst type.