Tailoring the active sites in Cu-SSZ-13 as a catalyst for the selective catalytic reduction of NH3 to minimize HCHO and HCN emissions

Synthetic fuels are promising candidates for achieving carbon neutrality and lowering soot formation. However, their combustion leads to notable amounts of formaldehyde and other oxygenates. These emissions further affect the selective catalytic reduction (SCR) of NOx and cause secondary HCN emissions due to their reaction with NH3. This study focuses on elucidating the structural features of Cu-SSZ-13—a widely applied NH3-SCR catalyst—that lead to high formaldehyde conversion while minimizing HCN emissions. Complementary in situ/operando characterization techniques supported by density functional theory calculations are systematically applied for a series of Cu-SSZ-13 catalysts with different Cu loadings and Si/Al ratios. The obtained results demonstrate that the decrease in SCR activity due to the presence of HCHO correlates with the formation of mobile Cu–CN species, whereas low HCN emissions at >350 °C are associated with the presence of ZCuOH species in the catalyst structure.