Studies on H2 assisted LPG reduction of NO over Ag/Al2O3 catalyst

Abstract

Hydrocarbon-Selective catalytic reduction (HC-SCR) is a potential method to remove NOx under excess oxygen conditions such as diesel engine exhausts and lean burn engines. Ag-Al 2 O 3 is a good catalyst for HC-SCR of NOx under lean-burn conditions. Further, addition of H 2 is effective for enhancing HC-SCR activity. This effect is unique to silver and to specific Ag/support combinations, namely, Ag/ δ- Al 2 O 3 .Therefore, in the present investigation, Ag/Al 2 O 3 catalyst containing 2.0 wt.% Ag was prepared by wet-impregnation method. The catalysts were characterized by various techniques like low temperature N 2 adsorption, XRD, XPS and SEM. Two different reductants CO and LPG were comparatively studied for SCR of NO over the Ag-Al 2 O 3 catalyst without and with H 2 -assisted. The experiments were performed in a fixed bed tubular down flow reactor under the following conditions: composition of gas mixture was 0.13% NO, 2.50% LPG/CO, 1% H 2 , 10% O 2, rest Ar; total flow rate of 60 ml/min, temperature varied from 50-400 o C and pressure 1 atm. High conversion of NO, around 100%, is achieved using LPG as a reductant with H 2 and without H 2 . Results showed that light off temperature of catalyst significantly reduced by the introduction of H 2 in feed stream with LPG reductant. The maximum conversions of NO with CO and LPG reductants were 35.15 and 97.79 % at 224 and 365 o C respectively. While, the maximum conversions with H 2 -LPG and H 2 -CO reductants were 100 and 99.46% at 117 and 220 o C respectively. Therefore, H 2 -LPG-SCR system can be used to get 100% NO reduction at low temperature. Very few studies are dedicated to LPG as reductant.