Hydrothermal aging alleviates hydrocarbon poisoning effects on high-silica Cu-SSZ-16 catalysts for NH3-SCR

Hydrocarbons (HCs) exert toxic effects on the activity of Cu-based zeolite catalysts for NH₃-SCR on diesel vehicles. This study investigated the hydrocarbon resistance of both fresh and hydrothermally aged high-silica Cu-SSZ-16 catalysts. It was found that low-temperature activity of Cu-SSZ-16 catalyst decreased after C₃H₆ poisoning, which was mainly due to the blockage of pore channels and the coverage of Cu active sites as well as acid sites by the formation of carbon deposits. Additionally, [Cu(OH)]⁺-Z was proposed to be more easily affected by C₃H₆ poisoning than Cu²⁺-2Z. Hydrothermally aged Cu-SSZ-16 presented better C₃H₆ resistance than the fresh catalyst since less carbon deposits were accumulated and [Cu(OH)]⁺-Z species were partially transformed to more-stable Cu²⁺-2Z in the aged sample. This was probably because of the reduction of acid sites and the formation of CuO_x, which enhanced the oxidation of C₃H₆, thereby inhibiting the formation of carbon deposits. In addition, the coverage of the active Cu species also influenced the adsorption and oxidation of NO, causing a decrease in low-temperature activity. Thus, the low-temperature activity could be fully recovered by hydrothermal treatment at 500 °C due to the removal of carbon deposits and recovery of Cu active sites as well as acid sites. In summary, high-silica Cu-SSZ-16, with high resistance to HCs and excellent hydrothermal stability, is a competitive candidate as a catalyst for the NH₃-SCR reaction in practical application.