Effect of alkali metal poisoning on Cu-SSZ-13 in selective catalytic reduction with ammonia (NH 3 -SCR)

Abstract

Cu-SSZ-13 is widely recognized as an efficient catalyst for the selective catalytic reduction of NO x with ammonia (NH 3 -SCR). However, in practical stationary applications, it is frequently exposed to alkali metal contaminants, which can significantly influence its catalytic performance. In this study, the effects of different alkali metal salts (NaNO 3 , KNO 3 , NaCl and KCl) on Cu-SSZ-13 were systemically investigated (regarding the variation in the physicochemical properties and NH 3 -SCR activity). A slight promotional effect (about 10% increase in NO x conversion) was observed at low temperatures (< 250 °C) for alkali metal poisoned samples, which is attributed to the enhanced presence of active ZCu II OH species, as evidenced by H 2 -TPR analysis. Conversely, a marked deactivation (up to 50% decline in NO x conversion) was observed at high temperatures (> 400 °C), primarily due to the loss of Brøsted acid sites and isolated Cu 2+ species, as indicated by NH 3 -TPD, pyridine-IR, H 2 -TPR and UVvis spectroscopy. Notably, alkali metal chlorides (KCl, NaCl) induced more severe deactivation than their nitrate counterparts, likely due to a synergistic effect between framework dealumination and transformation of Cu 2+ species, leading to the formation of CuAlO x species. These findings provide deeper insight into the effect of alkali metal poisoning on NH 3 -SCR activity of Cu-SSZ-13, highlighting the necessity of preventing alkali metal chlorides from entering SCR systems to maintain catalyst efficiency.