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

Abstract

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–SCR. Characterization results indicate that cocations weaken interactions between Cu ions and the CHA framework making them more readily reducible. By removing a portion of Bronsted 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...