Effect of washcoat pore structure on NOx conversion efficiency of SCR system

The effect of washcoat pore structure on NOx conversion efficiency was analyzed based on a SCR catalyst model and the ways to improve the efficiency were explored. The simulation results demonstrate that the effect of the washcoat pore structure on the NOx conversion efficiency of the SCR catalyst may be divided into activity limited region, pore diffusion limited region and film transfer limited region. In the activity limited region, the NOx conversion efficiency is limited by catalyst activity. The efficiency can be improved by reducing catalyst activity with increase of vanadium concentration or by increasing washcoat load.In the pore diffusion limited region, the NOx conversion efficiency is limited by diffusion rate of reactants of NOx and NH3 inside the washcoat pore.A good adjustment of pore structure leads to higher diffusion rate of the reactants, thus improving the NOx conversion efficiency. In the film transfer limited region, the NOx conversion efficiency is limited by the concentration of the reactants. Increase of geometrical surface area (GSA) can increase the contact between exhaust gas and washcoat, which can enhance the NOx conversion efficiency. ©, 2015, Chinese Society for Internal Combustion Engines. All right reserved.