Diesel DeNOx reduction

The Possibility of Modifying Thermal DeNOx Chemistry to suit Diesel Engines The Use of Other Radicals NH2 is not the only kind of radical known to be capable of reducing NO. Hydrogen abstraction from HNCO can form the free radical NCO which is known to react rapidly with NO, reducing it to N20. The initial report of the RAPRENOx process8 claimed that HNCO was capable of reducing NO at temperatures as low as 592°C,but subsequent work showed that reduction of NO by HNCO produces much more N20 than does the reduction with Nt and that the two processes have essentially identical temperature windows. Since the reaction sequence... 

The first of these requirements is obviously a problem. The Thermal DeNOx reaction is exothermic but only weakly so. If we assume that 600 ppm NO is reduced with 900 ppm NH3 and 1800 ppm H2, the rest of the exhaust gas having a composition of 10% 02, 6.9% C02, 6.2% H20, and balance nitrogen, the heat released by the reduction of the NO will provide a temperature increase of 42.5°F. While it is possible to raise the temperature of the exhaust gas by burning more fuel, the amount of fuel this requires is substantial. For an engine using a diesel fuel with an H/C ratio of 1.8, and a heat of formation of -5.5 kcal/mole of C, the additional fuel consumption needed to raise the exhaust gas temperature from 942.5°F to 1300°F, is 14.9% of the primary fuel consumption. 

The aim of this paper is to understand the influence of zinc on platinum catalytic behaviour. The added metal can either deactivate or provoke an increase in the catalytic activity of platinum either for reforming reactions or depollution reactions respectively, even when the gas atmosphere is always reductive. We shall study the influence -i) of the mode of preparation, -ii) of the zinc loading and -iii) of the kinetic parameters, on the activity of S-[Pt-Zn] catalysts in DeNOx reactions.The catalysts have been characterised by TPR, chemisorption and EXAFS and tested in the reaction of selective catalytic reduction (SCR) using diesel conditions. 

Currently, the major deNOx after-treatment technologies under consideration include the so-called Lean-NOx Traps (LNT), which are used with direct injection gasoline and Diesel engines, and the Selective Catalytic Reduction (urea-SCR) process. 

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