Studv On Ammonia Storage Model For SCR Catalyst And Its Application On Aging Assessment

Air pollution has been aggravated by nitrogen oxides (NOx) and particulate matter (PM) emissions from diesel engine, leading to more stringent diesel emission regulations. Thus, it’s urgent to reduce NOx emission from diesel engine. Currently, selective catalytic reduction (Urea-SCR), using urea as reductant, is considered as one of the most effective technologies to reduce NOx emission. However, SCR reaction model is still not perfect and there also exists some issues in its application, such as ammonia slip and catalyst aging. Therefore, ammonia storage model for SCR catalyst is presented in this study based on the research of NH3 adsorption-desorption reaction kinetics model. Then, the sdudy on steady ammonia storage characteristics, dynamic ammonia storage and aging assessment issues of SCR catalyst were studied based on ammonia storage model.First of all, the NH3 adsorption-desorption experiment was conducted on a fixed bed flow reactor. Single site and dual sites adsorption-desorption reaction kinetics model were well established and particle swarm optimization (PSO) was used to identify the model parameters. The results of NH3 adsorption-desorption experiment show that dual sites reaction kinetics model is more accuratly to describe the process of NH3 adsorption-desorption than single site reaction kinetics model.Secondly, on the basis of dual sites NH3 adsorption-desorption reaction kinetics model, ammonia storage model for SCR catalyst was established, which is suitable for washcoat honeycomb monolith catalyst. Identification of model parameters and validation of its general applicability were well studied by comparing to the results of NH3 adsorption-desorption experiment. The results from the research on the ammonia storage characteristics of SCR catalyst based on ammonia storage model show, saturated total storage amount increase with decreasing temperature and increasing inlet NH3 concentration, except space velocity. However, stable total storage amount increase with decreasing temperature and increasing space velocity, except inlet NH3 concentration. Besides, the time required for dynamic ammonia storage reduces with all of three factors increasing.Finally, ammonia storage model parameters for SCR catalyst after different levels of hydrothermal aging were re-identified by the results of NH3 adsorption-desorption experiment under 150℃. By comparing and analyzing different model parameters, it turns out that when the hydrothermal aging temperature increases, desorption activation energy of weak site almost remains consistent, while desorption activation energy of strong site decreases. Meanwhile, ammonia storage capacity of weak and strong site both decreases, porosity and effective diffusion coefficient of SCR catalyst also reduce. The results from the research on the ammonia storage characteristics of SCR catalyst after hydrothermal aging show that when the hydrothermal aging temperature increases, saturated total storage amount and stable total storage amount both decrease, the time required for dynamic ammonia storage also reduces.