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

Dye‐modified TiO 2 photocatalysts showed a high photocatalytic activity for the selective catalytic reduction of NO with NH 3 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 TiO 2 (NO conversion >99 %, N 2 selectivity >99 %). Diffuse reflectance infrared Fourier transform spectroscopy showed that nitrite (NO 2 − ) and nitrate (NO 3 − ) species were generated on the N3‐TiO 2 surface under visible‐light irradiation. In gas‐switching reactions, NO 2 − on the N3‐TiO 2 surface became N 2 by a reaction with adsorbed NH 3 under visible‐light irradiation, although NO 3 − reacted with NH 3 to form N 2 and N 2 O. Based on the reactivity with NH 3 , we concluded that the NO 2 − species is an intermediate in the selective photocatalytic reduction and reacts with NH 3 adsorbed on the surface of N3‐TiO 2 under visible‐light irradiation to form N 2 selectively.