Selective catalytic reduction of NO with NH3 over MnOx-CeO2 catalysts: The great synergy between CeO2 and crystalline phase of Mn3O4

MnOx-CeO2 catalysts have been widely investigated in the reaction of selective catalytic reduction of NO with NH3 (NH3-SCR). However, the existence of diverse Mn species together with multiple interfaces between MnOx and CeO2 precludes clear understanding of the synergy. Herein, by constructing MnOx-CeO2 catalysts with controlled dispersion and interface properties, the significant promotion effect of interfacial contact between CeO2 and crystalline Mn3O4 in NH3-SCR was revealed. Although dispersed MnOx exhibited the combined merits of strong interaction with CeO2, improved textural property and abundant adsorption sites for NO/NH3, the catalytic performance was still not superior. With advent of Mn3O4 crystallites, the NO conversion was much enhanced, demonstrating essential role of crystalline MnOx. Notably, loss of activity was also observed when apparent phase segregation between ceria and crystalline Mn3O4 occurred, emphasizing the importance of Mn3O4/CeO2 boundary. Further mechanism analyses from in situ NH3-DRIFTS, quantitative titration of surface NOx with NH3 and kinetics measurement disclosed the crucial role of crystalline Mn3O4 in activating NH3 for reaction with NOx anchored on ceria, greatly boosting the catalytic performance. The result of present study enriches our understanding on the synergism between MnOx and ceria in NH3-SCR.