Modeling Competitive Adsorption in Urea-SCR Catalysts for Enhanced Low Temperature NOx Control
Jong Lee, Pacific Northwest National Laboratory
Maruthi Devarakonda, Russell Tonkyn, Diana Tran, Jong H. Lee and Darrell Herling
Institute for Interfacial Catalysis, Pacific Northwest National Laboratory,
Richland, WA 99352, USA
Although the SCR technology exhibits higher NOx reduction efficiency over a wider range of temperatures among the lean NOx reduction technologies, further improvement in low-temperature performance is required to meet the future emission standards and to lower the system cost. In order to improve the catalyst technologies and optimize the system performance, it is critical to understand the reaction mechanisms and catalyst behaviors with respect to operating conditions. For example, it is well known that the ammonia coverage on catalyst surface is critical for NOx reduction efficiency. However, the level of ammonia storage is influenced by competitive adsorption by other species, such as H2O and NO2. Moreover, hydrocarbon species that slip through the upstream DOC during the cold-start period can also inhibit the SCR performance, especially at low temperatures. Therefore, a one-dimensional detailed kinetic model that can account for the effects of such competitive adsorption has been developed based on steady state surface isotherm tests on a commercial Fe-zeolite catalyst. The model has been written in C language and implemented as an S function in Matlab/Simulink environment. In addition, steady state experiments showing the impact of each of the adsorbents on various SCR reactions will be discussed.