T. Ibusuki et K. Takeuchi, REMOVAL OF LOW CONCENTRATION NITROGEN-OXIDES THROUGH PHOTOASSISTED HETEROGENEOUS CATALYSIS, Journal of molecular catalysis, 88(1), 1994, pp. 93-102
Titanium dioxide (TiO2) oxidized nitric oxide (NO) to nitric acid (HNO
3) very rapidly under ultraviolet light illumination, but some NO was
oxidized to nitrogen dioxide (NO2), while activated carbon (AC) adsorb
ed NO2 well. A mixture of TiO2 and AC was thus confirmed to be an exce
llent 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 th
e catalytic activity gradually declined with the reaction time, it cou
ld be completely recovered only by washing the catalyst with water, su
ggesting that HNO3 accumulated on the catalyst was removed. It is infe
rred 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.