Quantitative study of the adsorption sites and reaction mechanism of NH3-SCR on Cu-SSZ-39 and H-SSZ-39

Cu-SSZ-39 demonstrated exceptional resistance to hydrothermal aging during NH3-SCR. So far, the precise quantification of adsorption sites for various reactants on Cu-SSZ-39 remains uncertain. In this study, the quantitative analysis using a transient response method (TRM) allowed for determining the adsorption quantities of reactants, as well as the concentrations of various Cu species, and the reaction pathway on Cu-SSZ-39 and H-SSZ-39. Cu benefited N2 formation through NO reacting with adsorbed NH3, while NH4NO3 reacted with NO to form N2 instead of NO2 or N2O. On Cu-SSZ-39, the dominant pathway involved NO reacting with adsorbed NH3, resulting in the production of N2 and H2O, and another important pathway was “NH4NO3 fast path” (NH4NO3 + NO + *-ONH4 + * → 2 N2 + 3 H2O + 2 *-OH). O2 facilitated the reaction between NO and NH3. The numbers of Z2Cu2+and ZCu-OH were also determined by TRM. More Z2Cu2+ species caused its high hydrothermal stability.