Cooperation of Pt/Al 2O 3 and In/Al 2O 3 catalysts for NO reduction by propene in lean burn condition

Abstract

The Pt/Al 2O 3, In-Al 2O 3 and binary Pt-In/Al 2O 3 catalysts were prepared by a single sol–gel method. Their physical properties were characterized by BET, XRD, XPS and TPD, and their activities for selective catalytic reduction of NO with propene in the presence of oxygen were studied. The results showed that the inhibition by H 2O and SO 2 is reversible over Pt/Al 2O 3, whereas it is irreversible over In/Al 2O 3. In order to improve the activity and temperature window, various kinds of combined catalyst systems, such as physically mixed, two-stage, and intermediate addition reductants (IAR), for NO reduction by propene were investigated; the effects of H 2O and SO 2 on the activity and temperature window were also discussed. The results showed that the activities and temperature windows were obviously improved for both two-stage and IAR combined catalysts, but no cooperation effects were observed over binary Pt-In/Al 2O 3 catalyst or over physically mixed Pt/Al 2O 3 and In/Al 2O 3 combined catalysts. It was found that coexisting water vapor enhanced the catalytic activity at the medium temperature of 300–400 °C over a two-stage catalyst of In/Al 2O 3 and Pt/Al 2O 3 in series. Intermediate addition of propene between a Pt/Al 2O 3 oxidation and an In/Al 2O 3 reduction combined catalyst system showed high NO reduction activity in a wider temperature window. The NO conversion was above 60% in the temperature range of 300–500 °C, and the maximum NO conversion was 91% even in the presence of 2% H 2O and 100 ppm SO 2.