Two-stage catalyst system for selective catalytic reduction of NOx by NH3 at low temperatures

Abstract Three catalysts, 1 wt.% Pt/Al 2 O 3 , 20 wt.% Cu/Al 2 O 3 , and 1 wt.% Pt–20 wt.% Cu/Al 2 O 3 were evaluated for the oxidation of NO by O 2 and the selective catalytic reduction (SCR) of NO x by NH 3 in the absence and presence of H 2 O. The Pt/Al 2 O 3 catalyst exhibited the largest values in NO oxidation efficiency and NO x removal efficiency among the three catalysts. The presence of H 2 O caused a drop in the NO oxidation and the SCR activities. The SCR performance was significantly improved when Pt/Al 2 O 3 and Cu/Al 2 O 3 catalysts were employed sequentially in a reactor. The highest SCR performance was achieved using two separate stages: oxidation of NO by O 2 over the Pt/Al 2 O 3 catalyst followed by reduction of NO 2 by NH 3 over the Cu/Al 2 O 3 catalyst. Under the condition with H 2 O, the two-stage catalyst system showed NO x removal efficiency over 80% at low temperatures below 200 °C, which was the highest value among the catalyst systems used in this study. The physical and chemical properties of the catalysts were determined using nitrogen adsorption, XRD, TPR, and pulse CO chemisorption experiments.