Activating low-temperature NH3-SCR catalyst by breaking the strong interface between acid and redox sites: A case of model Ce2(SO4)3-CeO2 study

The occurrence of NH3-SCR (selective catalytic reduction of NO with NH3) reaction on catalyst surface typically requires acid and redox sites. However, the role of acid-redox interaction on NH3-SCR performance is still obscure due to complex acidities and entangled acid-redox sites. Herein, three types of model Ce2(SO4)3-CeO2 catalysts with distinct interfaces are constructed to reveal the effect of acid-redox interaction on NH3-SCR performance. That is, SO42-/CeO2-VS (vapor sulfation of ceria) with strong acid-redox interfacial contact, SO42-/CeO2-WI (wet impregnation), and SO42-/CeO2-SG (solid grinding) with limited interfaces. It is found the redox property is significantly disturbed as a result of the electron-withdrawing effect from the sulfate. Theoretical result unravels that the introduction of Ce2(SO4)3 retards the oxygen vacancy formation over CeO2. Due to restricted interfaces in SO42-/CeO2-SG, the negative influence from acid sites is greatly alleviated. Further mechanism study discloses the weakened acid-redox interaction actually changes the nature of surface NOx species, resulting in the generation of reactive species (*O-N-O* and cis-N2O22-) and the promotion of surface reaction via Langmuir-Hinshelwood (L-H) mechanism.