Rationally tailored redox ability of Sn/γ-Al 2 O 3 with Ag for enhancing the selective catalytic reduction of NO x with propene.

The development of excellent selective catalytic reduction (SCR) catalysts with hydrocarbons for lean-burn diesel engines is of great significance, and a range of novel catalysts loaded with Sn and Ag were studied in this work. It was found that the synergistic effects of Sn and Ag enabled the 1Sn5Ag/γ-Al 2 O 3 (1 wt% Sn and 5wt% Ag) to exhibit superior C 3 H 6 -SCR performance. The de-NO x efficiency was maintained above 80% between 336 and 448 °C. The characterization results showed that the presence of AgCl crystallites in the 1Sn5Ag/γ-Al 2 O 3 catalyst helped its redox ability maintain an appropriate level, which suppressed the over-oxidation of C 3 H 6 . Besides, the number of surface adsorbed oxygen (O α ) and hydroxyl groups (O γ ) were enriched, and their reactivity was greatly enhanced due to the coexistence of Ag and Sn. The ratio of Ag 0 /Ag + was increased to 3.68 due to the electron transfer effects, much higher than that of Ag/γ-Al 2 O 3 (2.15). Lewis acid sites dominated the C 3 H 6 -SCR reaction over the 1Sn5Ag/γ-Al 2 O 3 catalyst. The synergistic effects of Sn and Ag facilitated the formation of intermediates such as acetates, enolic species, and nitrates, and inhibited the deep oxidation of C 3 H 6 into CO 2 , and the C 3 H 6 -SCR mechanism was carefully proposed.