SCR Deactivation Kinetics for Model-Based Control and Accelerated Aging Applications

Selective Catalytic Reduction (SCR) catalysts are used to reduce NO_x emissions from internal combustion engines in a variety of applications. Southwest Research Institute (SwRI) performed an Internal Research & Development project to study SCR catalyst thermal deactivation. The study included a V/W/TiO₂ formulation, a Cu-zeolite formulation and a Fe-zeolite formulation. This work describes NH₃ storage capacity measurement data as a function of aging time and temperature. Addressing one objective of the work, these data can be used in model-based control algorithms to calculate the current NH₃ storage capacity of an SCR catalyst operating in the field, based on time and temperature history. The model-based control then uses the calculated value for effective DEF control and prevention of excessive NH₃ slip. Addressing a second objective of the work, accelerated thermal aging of SCR catalysts may be achieved by elevating temperatures above normal operating temperatures. Time and temperature correlations use the Arrhenius equation, which requires a formulation-specific deactivation energy value (Ed). The NH₃ storage capacity data generated in this work were used to calculate an Ed value for each of the three SCR catalyst formulations.