Sulfur Poisoning of a Cu-SSZ-13 SCR Catalyst under Simulated Diesel Engine Operating Conditions

Cu-SSZ-13 catalysts are widely used for diesel aftertreatment applications for NO_x (NO and NO₂) abatement via selective catalytic reaction (SCR) due to their high conversion efficiency and excellent hydrothermal stability. Diesel engine exhaust contains small amounts of SO_x due to the combustion of sulfur compounds in diesel fuel. The engine out SO_x level mainly depends on the sulfur content in the diesel fuel. The presence of SO_x from engine exhaust can deteriorate the SCR performance of Cu-SSZ-13 catalysts in real-world applications. This work is focused on the sulfur-induced deactivation process of a Cu-SSZ-13 catalyst under a range of simulated diesel engine operating conditions. Two catalyst deactivation modes, namely chemical poisoning and physical poisoning, are identified, primarily depending on the operating temperature. Chemical poisoning mainly results from the interaction between SO_x and Cu species within the zeolite framework. Physical poisoning is a consequence of the accumulation of ammonium (bi) sulfate formed from the interaction between SO_x and NH₃, especially at low temperature conditions. Temperature programmed desorption (TPD) experiments were conducted to characterize the deactivated catalyst. In addition, a modeling approach was applied to quantify the deactivation process as well as the decomposition of the sulfur species on the poisoned catalyst to optimize the catalyst reactivation strategy.