Experimental Study on the Effects of the Exhaust Atmosphere on SO2 Poisoning over the Cu-SSZ-13 SCR Catalyst

Cu-SSZ-13 has been used as the main catalyst in selective catalytic reduction (SCR) systems for diesel because of its excellent hydrothermal stability and SCR activity. SO2 poisoning is one of the main factors affecting the SCR activity of Cu-SSZ-13 at low temperatures. The effects of the actual exhaust atmosphere on the characteristics of SO2 poisoning were experimentally investigated. In the absence of NH3, CuSO4 species generated at Cu sites gradually increased with an increase in the SO2 poisoning temperature, while the amount of H2SO4 species was stable below 350 °C. The SCR NOx conversions of samples SO2 poisoned at 250 °C was lower than those of samples poisoned at both 150 and 400 °C. In the presence of NH3, (NH4)2SO4 species were generated, and more importantly, the production of CuSO4 species was significantly promoted, which substantially reduced SCR NOx conversions for the samples poisoned at 150 and 250 °C. When the SO2 poisoning temperature was 400 °C, NH3 inhibited CuSO4 species generation, and NOx conversions were basically unchanged. The SO2-poisoned Cu-SSZ-13 catalyst can recover most of its activity at high regeneration temperatures above 650 °C, but the regeneration temperature can be reduced to 450 °C, and all sulfate species can be decomposed while NH3 is present during regeneration.