Mechanism study on TiO2 inducing •O2- and O•H radicals in O3/H2O2 system for high-efficiency NO oxidation

To achieve high NO oxidation efficiency, excessive O-3 must be used, which would lead to the high cost and escape of ozone. Herein, we adopted low cost and environmental-friendly TiO2 as the catalyst of low concentration O-3 and H2O2 system for high-efficiency NOx oxidation. The Ti sites on TiO2 were the deprotonation sites of H2O2 and H2O into Ti-OOH and Ti-OH species, respectively. We found that the surface of rutile phase TiO2 had a low concentration Ti-OOH component but a large amount of Ti-OH after contacting with H2O2 solution, thus lots of (OH)-O-center dot and a few O-center dot(2)- radicals formed with introducing O-3 molecules. H2O2 solution induced the formation of a large amount of Ti-OOH and Ti-OH species on the anatase phase TiO2 surface, thus lots of O-center dot(2)- generated in the O-3/H2O2 system. O-center dot(2)- and (OH)-H-center dot radicals could efficiently oxidize NO, in which O-center dot(2) - radicals could oxidize NO to NO3- in one step with high selectively. Therefore, anatase TiO2 had better performance in NOx oxidation than rutile phase TiO2. The effect of temperature and SO2 concentration on NO oxidation was also investigated, the results showed that TiO2-A/O-3/H2O2 system promoted NO oxidation at a low temperature and a low concentration of SO2.