Abstract
Keywords:
SCR, syngas, hydrogen, Pt catalyst
Abstract
The selective catalytic reduction of NOx by syngas or hydrogen was carried out at the engine exhaust gas temperatures of 100 - 150 °C over Pt/Al2O3 catalysts. The gas mixture containing 2083 ppm of NO, 5% of O2 and N2 balance was used. When syngas was introduced (CO 2000 ppm and H2 2000 ppm) to the reactant mixture, only 14% of NO was reduced at 110 °C over a 0.3 wt.% Pt catalyst and the reduced products were N2 and N2O. In the case of hydrogen (10000 ppm) injection, some NO (about 25%) was converted either N2O or NO2 depending on the reduction state of Pt even at the room temperature (cold start condition), N2O being predominantly produced by the Pt catalyst in a reduced form and NO2 formed by the oxidized Pt catalyst. At temperatures between 50 and 150 °C, N2 and N2O were the products of NO reduction by H2. The temperature window of the high NO conversion (80% or higher) varied with the Pt loading of the catalyst. The active temperature window was lower for a higher loading Pt catalyst. The selectivity of reduction products also changed with the temperature. At temperatures below 100 °C with higher-loading Pt catalysts, 80% of NO was converted to N2O and only 20% was reduced to N2. However, at temperatures between 100 °C and 150 °C over a 0.02 wt.% Pt catalyst, the N2 selectivity reached to about 50%.