Visible-light-assisted selective catalytic reduction of NO with NH3 on porphyrin derivative-modified TiO2 photocatalysts

Porphyrin-derivative-modified TiO2 photocatalysts showed high photocatalytic activity for the selective catalytic reduction of NO with NH3 in the presence of O-2 under visible-light irradiation. Tetra(p-carboxyphenyl) porphyrin (TCPP) was the most effective photosensitizer among the five porphyrin derivatives investigated. NO conversion and N-2 selectivity of 79.0% and 100%, respectively, were achieved at a gas hourly space velocity of 50 000 h(-1). UV-Vis and photoluminescence spectroscopies revealed the presence of two species of TCPP on the TiO2 surface; one was a TCPP monomer and the other was an H-aggregate of the TCPP molecules. It was concluded that the TCPP monomer is an active species for the photo-assisted selective catalytic reduction (photo-SCR). Moreover, an increase in the fraction of H-aggregates with increasing TCPP loading amount resulted in a decrease in the photocatalytic activity of the photo-SCR.