Selective catalytic reduction of NO x with C 3H 6 over an Ag/Al 2O 3 catalyst with a small quantity of noble metal

Abstract

The selective catalytic reduction of NO x with C 3H 6 (C 3H 6-SCR of NO x ) was carried out in the presence of water vapor over various trace noble metal (Pt, Au and Pd) co-impregnated with Ag/Al 2O 3 catalysts. The Ag–Pd (0.01%)/Al 2O 3 shows a higher NO x conversion than Ag/Al 2O 3 does, especially at temperatures ranging from 300 to 500 °C. However, the additions of Au and Pt to Ag/Al 2O 3 only resulted in a decrease of activity for the C 3H 6-SCR of NO x . In situ DRIFTS spectra suggests that the presence of trace Pd (0.01%) catalyzed the formation of an enolic species which was converted from C 3H 6, whereas the presence of Pt and Au did not show this effect. The surface enolic species is very active towards NO 2 and NO 3 −, resulting in the formation of an NCO species which is the key reaction intermediate in the selective catalytic reduction of NO x .