To reveal the role of impregnated sodium (Na) ions in Cu/SSZ-13 catalysts, Cu/SSZ-13 catalysts with four Na-loading contents were prepared using an incipient wetness impregnation method and hydrothermally treated at 600 °C for 16 h. The physicochemical property and selective catalytic reduction (SCR) activity of these catalysts were studied to probe the deactivation mechanism. The impregnated Na exists as Na⁺ on catalysts and results in the loss of both Brönsted acid sites and Cu²⁺ ions. Moreover, the high loading of Na ions destroy the framework structure of Cu/SSZ-13 and forms new phases (SiO₂/NaSiO₃ and amorphous species) when Na loading was higher than 1.0 mmol/g. The decreased Cu²⁺ ions finally transformed into Cu_xO, CuO, and CuAlO_x species. The inferior SCR activity of Na impregnated catalysts was mainly due to the reduced contents of Cu²⁺ ions at kinetic temperature region. The reduction in the amount of acid sites and Cu²⁺ ions, as well as copper oxide species (Cu_xO and CuO) formation, led to low SCR performance at high temperature. Our study also revealed that the existing problem of the Na ions’ effect should be well-considered, especially at high hydrothermal aging when diesel particulate filter (DPF) is applied in upstream of the SCR applications.

The preserved Pd ions as γ and β sites related with Al at T1–T2 sites corresponded to the stabilized NO_x storage capability and rendered a suitable desorption temperature.