The effect of H2 and CO on the selective catalytic reduction of NO, under real diesel engine exhaust conditions over Pt/Al2O3

In the presented work the selective catalytic reduction (SCR) of NOx in a real diesel engine exhaust gas (02 present) from the engine operating at different conditions with and without H-2 and CO additions were studied. The tests were carried out using real diesel engine exhaust gas over 1%Pt supported on alumina (Al2O3). The catalyst exhibits good NOx reduction activity at a narrow temperature range of 200 to 300 degrees C when there is only a HC present. The maximum NOx reduction of around 60% was achieved at temperature of 260 degrees C. Although, the engine operating with EGR improves the percentage of NOx converted in the SCR system due to increased HC:NOx ratio and reduced NOx concentration in the engine exhaust gas, the number of NOx-pprn reduced over the catalyst was reduced. The cause of this effect is not yet clear, but there are evidences that this attributes to (a) lower NOx coverage on the catalyst surface, which in turn makes its reduction by HC less probable and (b) the increased soot emissions which are blocking part of the catalyst active sites that are active in reducing NOx. Hydrogen addition expands the SCR activity window towards lower temperatures (100-300 degrees C) without affecting the maximum NOx conversion. In contradiction to H-2 the CO addition is favourable to the H-2 oxidation reaction and the poisoning of the catalysts active sites and the good low temperature NOx reduction activity cannot be seen. The incorporation of a mini-exhaust gas-reformer on-board a vehicle to provide the H-2 in the SCR reactor will require catalyst design and reactor engineering to maximise H-2 production and eliminate CO with the minimum penalty in the fuel economy. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.