Rationally tailored redox ability of Sn/γ-AlO with Ag for enhancing the selective catalytic reduction of NO 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-AlO (1 wt% Sn and 5wt% Ag) to exhibit superior CH-SCR performance. The de-NO efficiency was maintained above 80% between 336 and 448 °C. The characterization results showed that the presence of AgCl crystallites in the 1Sn5Ag/γ-AlO catalyst helped its redox ability maintain an appropriate level, which suppressed the over-oxidation of CH. Besides, the number of surface adsorbed oxygen (O) and hydroxyl groups (O) were enriched, and their reactivity was greatly enhanced due to the coexistence of Ag and Sn. The ratio of Ag/Ag was increased to 3.68 due to the electron transfer effects, much higher than that of Ag/γ-AlO (2.15). Lewis acid sites dominated the CH-SCR reaction over the 1Sn5Ag/γ-AlO 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 CH into CO, and the CH-SCR mechanism was carefully proposed.