Rationally tailored redox ability of Sn/γ-Al2O3 with Ag for enhancing the selective catalytic reduction of NOx 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/gamma-Al2O3 (1 wt% Sn and 5wt% Ag) to exhibit superior C3H6-SCR performance. The de-NOx efficiency was maintained above 80% between 336 and 448 degrees C. The characterization results showed that the presence of AgCl crystallites in the 1Sn5Ag/gamma-Al2O3 catalyst helped its redox ability maintain an appropriate level, which suppressed the over-oxidation of C3H6. Besides, the number of surface adsorbed oxygen (O-alpha) and hydroxyl groups (O-gamma) 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/gamma-Al2O3 (2.15). Lewis acid sites dominated the C3H6-SCR reaction over the 1Sn5Ag/gamma-Al2O3 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 C3H6 into CO2, and the C3H6-SCR mechanism was carefully proposed.

Automated summary

The synergistic effects of Sn and Ag in the 1Sn5Ag/gamma-Al2O3 catalyst greatly enhance its C3H6-SCR performance. The presence of AgCl crystallites helps maintain an appropriate redox ability and suppresses over-oxidation of C3H6. The coexistence of Ag and Sn increases the reactivity of surface adsorbed oxygen and hydroxyl groups, and the electron transfer effects increase the ratio of Ag-0/Ag+.