REMOVAL OF LOW CONCENTRATION NITROGEN-OXIDES THROUGH PHOTOASSISTED HETEROGENEOUS CATALYSIS

Titanium dioxide (TiO2) oxidized nitric oxide (NO) to nitric acid (HNO3) very rapidly under ultraviolet light illumination, but some NO was oxidized to nitrogen dioxide (NO2), while activated carbon (AC) adsorbed NO2 well. A mixture of TiO2 and AC was thus confirmed to be an excellent photoassisted catalyst for removal of low concentration (sub-ppm) NO(x) from air. Addition of 1-3 wt.% of ferric oxide (Fe2O3) to the mixture could markedly increase the catalytic activity. Even though the catalytic activity gradually declined with the reaction time, it could be completely recovered only by washing the catalyst with water, suggesting that HNO3 accumulated on the catalyst was removed. It is inferred that the photoilluminated TiO2 generates reactive oxygen species which oxidize (NO and NO2) to (NO2 and HNO3). AC can trap NO2 and give TiO2 enough time to oxidize NO2 to HNO3. Fe2O3 seems to be a promoter which can attract more NO/NO2 to the surface of the catalyst.