Role of Ce in promoting low-temperature performance and hydrothermal stability of Ce/Cu-SSZ-13 in the selective catalytic reduction of NO_x with NH₃

With the increase of car ownership, new challenges are posed to the treatment of mobile source exhaust gas, especially denitration (de-NO_x). It is urgent to develop highly efficient de-NO_x catalyst with a wide working temperature window. In this work, a series of Ce modified Cu-SSZ-13 molecular sieves (Ce/Cu-SSZ-13) are prepared by ion exchange method with different exchange times (x = 1, 2, 4, 8 h), and the role of Ce in promoting low-temperature de-NO_x performance and hydrothermal stability of Ce/Cu-SSZ-13 in the selective catalytic reduction (SCR) of NO_x are investigated. Both the low-temperature de-NO_x performance and the hydrothermal stability of Cu-SSZ-13 are enhanced due to the modification of Ce, especially the Ce/Cu-SSZ-13 with an exchange time of 2 h. Both Ce/Cu-SSZ-13 and Cu-SSZ-13 present more than 95 % NO_x conversion in the temperature region of 210–600 °C, and Ce modification significantly improves the NO_x conversion in the low-temperature range (120–210 °C). It is revealed that the acidity, the surface Cu²⁺/Cu⁺ ratio and the NH₃ adsorption amount on Cu-SSZ-13 increase after Ce ion exchange, and the active component Cu²⁺ migrates to the more stable six-membered ring due to the modification of Ce, all of which have promote the improvement of NH₃-SCR de-NO_x performance. Furthermore, in the process of hydrothermal aging, the presence of Ce protects the framework of Cu-SSZ-13, acidic sites and active component Cu²⁺, which greatly improves the hydrothermal stability of Cu-SSZ-13 molecular sieve. In addition, in-situ DRIFTS shows that the developed Ce/Cu-SSZ-13 follows dual mechanisms of Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) to undergo NH₃-SCR reaction. This work provides a new idea for improving the low-temperature de-NO_x performance and hydrothermal stability of Cu-SSZ-13.