Numerical Simulation Of Catalytic Reduction Of Automotive Exhaust NO_x

Nitrogen oxides (NOx) is one of the major pollutants in automotive exhaust gases. It is difficult to remove, especially for lean-burn gasoline engines and diesel engines. The abatement of NOx has been a hot topic of study over the world. Lean-burn gasoline engines and diesel engines cannot meet the future stringent regulation by improving the internal combustion only. The introduction of exhaust gas aftertreatment systems must be brought about to meet the Euro IV standards and higher standards. Traditional three way catalyst cannot reduce NOx in lean-burn gasoline engines and diesel engines exhaust gas, which is oxidizing. NOx storage and reduction (NSR) and Selective catalytic reduction (SCR) are promising exhaust gas aftertreatment technology that efficiently reduce NOx under lean-burn conditions. A promising approach for a sulphur-resistant DeNOx catalyst was suggested by Nakatsuji. A rhodium-based catalyst operated under periodic lean-rich condition appears to be highly active towards NOx reduction.Nitrogen oxides reduction during rich period of NSR and Nakatsuji decomposition catalyst was investigated in this paper. Microkinetic was used to develop an elementary reaction mechanism, which describes the surface reaction precesses of reduction of NO by CO and H2 on rhodium. The identical NO reduction mechanism was supposed in CO-NO and H2-NO. The pre-exponential and activation energy of CO desorption was taken as coverage-dependent based on the experimental investigation of CO-NO reaction system. Also the reaction path analysis and systematic sensitivity were carried out to identify the critical kinetic steps for CO-NO and H2-NO reaction system, respectively.Furthermore, a detailed mechanism of SCR reaction in Urea-SCR system was discussed in this paper. The mechanism was implemented into the Perfectly Stirred Reactor (PSR) and Honeycomb Monolith Reactor model in CHEMKIN software package to simulate the SCR system. The concentration of NH3, NO, H2O and surface species was analyzed.