A Case Study of a Cu-SSZ-13 SCR Catalyst Poisoned by Real-World High Sulfur Diesel Fuel

To meet increasingly stringent diesel engine emission regulations, diesel engines are required to use ultra-low sulfur diesel (ULSD) and are equipped with advanced aftertreatment systems. Cu-SSZ-13 zeolite catalysts are widely used as selective catalytic reduction (SCR) catalysts due to their high NO_x reduction and excellent hydrothermal stability. However, active Cu sites of Cu-SSZ-13 catalysts can be poisoned by exposure to engine exhaust sulfur species. This poison effect can be mitigated with the use of ULSD and high temperature exposure from engine operation. On the other hand, ULSD is still not universally available where regulations require it, and vehicles may inadvertently operate with high sulfur diesel fuel (HSD) in some locations. The high concentration of exhaust sulfur species resulting from HSD combustion may rapidly poison the Cu-SSZ-13 SCR catalyst. In this study, the catalytic performance of a sulfur poisoned Cu-SSZ-13 SCR catalyst is analyzed. Results show that the as received SCR catalyst displays substantially low NO_x conversion below 350 °C. A thermal treatment at 550 °C can recover most of its lost performance. Temperature programmed desorption (TPD), BET surface area and thermo-gravimetric analysis (TGA) were applied to analyze the poisoned SCR catalyst. The results indicate that both physical poisoning and chemical poisoning contribute to the reduced NO_x conversion. In addition, reactivation experiments were conducted by progressively increasing the thermal treatment temperature to understand the effect of physical and chemical poisoning. Kinetic analysis was conducted to quantify catalyst deactivation and its recovery process.