Effects of Alkali and Alkaline Earth Cocations on the Activity and Hydrothermal Stability of Cu/SSZ-13 NH3鈥揝CR Catalysts

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• 作者：Feng Gao ; Yilin Wang ; Nancy M. Washton ; M谩rton Koll谩r ; J谩nos Szanyi ; Charles H. F. Peden
• 刊名：ACS Catalysis
• 出版年：2015
• 出版时间：November 6, 2015
• 年：2015
• 卷：5
• 期：11
• 页码：6780-6791
• 全文大小：679K
• ISSN：2155-5435

文摘

Using a three-step aqueous solution ion-exchange method, cocation modified Cu/SSZ-13 SCR catalysts were synthesized. These catalysts, in both fresh and hydrothermally aged forms, were characterized with several methods including temperature-programmed reduction by H₂ (H₂-TPR), temperature-programmed desorption of NH₃ (NH₃-TPD), and ²⁷Al solid-state nuclear magnetic resonance (NMR) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopies. Their catalytic performance was probed using steady-state standard NH₃鈥揝CR. Characterization results indicate that cocations weaken interactions between Cu ions and the CHA framework making them more readily reducible. By removing a portion of Br酶nsted acid sites, cocations also help to mitigate hydrolysis of the zeolite catalysts during hydrothermal aging as evidenced from ²⁷Al NMR. Reaction tests show that certain cocations, especially Li⁺ and Na⁺, promote low-temperature SCR rates while others show much less pronounced effects. In terms of applications, our results indicate that introducing cocations can be a viable strategy to improve both low- and high-temperature performance of Cu/SSZ-13 SCR catalysts.