Role of Ce in promoting low-temperature performance and hydrothermal stability of Ce/Cu-SSZ-13 in the selective catalytic reduction of NOx with NH3
SEPARATION AND PURIFICATION TECHNOLOGY(2023)
摘要
With the increase of car ownership, new challenges are posed to the treatment of mobile source exhaust gas, especially denitration (de-NOx). It is urgent to develop highly efficient de-NOx 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 pro-moting low-temperature de-NOx performance and hydrothermal stability of Ce/Cu-SSZ-13 in the selective cat-alytic reduction (SCR) of NOx are investigated. Both the low-temperature de-NOx 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 % NOx conversion in the temperature region of 210-600 degrees C, and Ce modification significantly improves the NOx conversion in the low-temperature range (120-210 degrees 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-NOx 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 fol-lows 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-NOx performance and hydrothermal stability of Cu-SSZ-13.
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关键词
Selective catalytic reduction,Cu-SSZ-13,De-NOx,Hydrothermal stability,Ion exchange
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