Potassium deactivation of Cu-SSZ-13 catalyst for NH3-SCR: Evolution of salts, zeolite and copper species

Cu-SSZ-13, as an efficient catalyst for NOx removal, has been commercialized in diesel exhaust aftertreatments. However, SCR catalysts in practical applications may suffer from alkali deactivation due to the introduction of engine oil additives and biodiesel. In this study, the poisoning effect of different potassium salts (K2CO3, K2SO4 and K3PO4) on the Cu-SSZ-13 catalyst was systematically investigated. Deactivation effect of potassium salts follows the order of K2CO3 > K2SO4 > K3PO4, resulting from the transformation of isolated Cu2+ into other copper species. The loss of isolated Cu2+ is considered as the main reason for the low-temperature deactivation while the formed copper oxides, copper sulfate and copper phosphate related species are mainly responsible for the different catalytic behaviors of the poisoned catalysts at high temperatures (>400 °C). The CuOx clusters induced by K2CO3 promote NH3 oxidation while the copper salts derived from K2SO4 and K3PO4 are relative inactive for this competitive reaction. As a balance between the consumption of NH3 by the side reaction and loss of Bronsted acid sites, the K2CO3 poisoned catalyst shows significantly dropped high-temperature SCR activity, while the reaction is promoted over those catalysts impregnated with K2SO4 and K3PO4 at high temperatures.