Selective Catalytic Reduction of NO in the Exhaust Using Syngas as Reducing Agent

摘要

The selective catalytic reduction of NO{sub}x by syngas or hydrogen was carried out at the engine exhaust gas temperatures of 100 - 150°C over Pt/Al{sub}2O{sub}3 catalysts. The gas mixture containing 2083 ppm of NO, 5% of O{sub}2 and N{sub}2 balance was used. When syngas was introduced (CO 2000 ppm and H{sub}2 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 N{sub}2 and N{sub}2O. In the case of hydrogen (10000 ppm) injection, some NO (about 25%) was converted either N{sub}2O or NO{sub}2 depending on the reduction state of Pt even at the room temperature (cold start condition), N{sub}2O being predominantly produced by the Pt catalyst in a reduced form and NO{sub}2 formed by the oxidized Pt catalyst. At temperatures between 50 and 150°C, N{sub}2 and N{sub}2O were the products of NO reduction by H{sub}2. 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 N{sub}2O and only 20% was reduced to N{sub}2. However, at temperatures between 100°C and 150°C over a 0.02 wt.% Pt catalyst, the N{sub}2 selectivity reached to about 50%.