Visible-Light-Assisted Selective Catalytic Reduction of Nitric Oxide with Ammonia over Dye-Modified Titania Photocatalysts

Dye-modified TiO2 photocatalysts showed a high photocatalytic activity for the selective catalytic reduction of NO with NH3 in the presence of O-2 under visible-light irradiation. Among the 15 dyes investigated, the maximum conversion was achieved using a Ru(2,2-bipyridyl-4,4-dicarboxylic acid)(2)(NCS)(2) complex (N3-dye) for the modification of TiO2 (NO conversion >99%, N-2 selectivity >99%). Diffuse reflectance infrared Fourier transform spectroscopy showed that nitrite (NO2-) and nitrate (NO3-) species were generated on the N3-TiO2 surface under visible-light irradiation. In gas-switching reactions, NO2- on the N3-TiO2 surface became N-2 by a reaction with adsorbed NH3 under visible-light irradiation, although NO3- reacted with NH3 to form N-2 and N2O. Based on the reactivity with NH3, we concluded that the NO2- species is an intermediate in the selective photocatalytic reduction and reacts with NH3 adsorbed on the surface of N3-TiO2 under visible-light irradiation to form N-2 selectively.