CeO2/H-SSZ-13 composite NH3-SCR catalysts achieve unprecedented high-temperature N2 selectivity

A series of CeO₂/H-SSZ-13 composite catalysts with CeO₂ contents ranging from 5 to 50 wt% are investigated. The catalysts are characterized using various techniques, including XRD, SEM, TEM, XPS, H₂-TPR, Raman spectroscopy and chemical titrations coupled with TPD and DRIFTS. Their catalytic performance is evaluated through steady-state NH₃-SCR. DFT calculations are also applied to supplement experimental data. The results demonstrate that the synergistic interactions between the redox domain (CeO₂) and the acid domain (H-SSZ-13) render the composite catalysts with excellent medium-to-high-temperature deNO_x efficiency. Notably, the formation of the unwanted N₂O side product is completely eliminated over these composite catalysts. By systematically regulating redox and acid functions, it is revealed that CeO₂ serves as the key active component for the rate-determining NO activation step, while H-SSZ-13 facilitates NH₃ adsorption and the decomposition of reactive intermediates. Based on detailed studies of SCR kinetics, N₂O formation, chemical trapping, as well as DFT calculations, it is proposed that the gaseous nitrite precursor HONO acts as the key reaction intermediate.