Revealing the mechanism of K-enhanced Cu-SSZ-13 catalysts against hydrothermal aging and P-poisoning for NOx reduction by NH3-SCR

Abstract

Cu-SSZ-13 (Cu-Z) has been commercialized as an efficient catalyst for NOx removal in mobile sources. However, in practical applications, the catalyst faces problems of poisoning (K and P) and hydrothermal aging. Therefore, in this work, we investigated the effects of K on P poisoning and hydrothermal aging in Al-rich Cu2/Z (2 wt% Cu). The presence of 1 wt% K could not only improve the high-temperature activity, which could reach above 99% at 225–600 °C on the K1/Cu2/Z, but also enhanced the hydrothermal stability and the resistance of P poisoning. Combing with a series of characterizations, K was mainly present in the Brӧnsted acid sites in the CHA cage, which led to the transformation of part of Z-[Cu(OH)]+ to Z2-Cu2+, reducing dealumination and the formation of CuOx and CuAl2O4 species during hydrothermal aging. Moreover, the presence of K could inhibit the formation of Cu-PO3-/PO43- species by P poisoning of Z-[Cu(OH)]+ species. In-situ DRIFTS results showed that the catalysts followed both E-R and L-H mechanism at 150 ℃. K doping could promote the formation of nitrate species and thus favoring the L-H mechanism, which probably enhanced the NH3-SCR activity.