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

• Three MnOx-CeO 2 catalysts with controlled surface and interfacial properties are prepared for investigation. • Strong interface between dispersed MnOx and CeO 2 does not show the best NH 3 -SCR performance. • The unique role of crystalline Mn 3 O 4 in promoting NH 3 activation is revealed. • The catalytic performance can be considerably improved by the synergistic interaction between crystalline Mn 3 O 4 and CeO 2. MnOx-CeO 2 catalysts have been widely investigated in the reaction of selective catalytic reduction of NO with NH 3 (NH 3 -SCR). However, the existence of diverse Mn species together with multiple interfaces between MnOx and CeO 2 precludes clear understanding of the synergy. Herein, by constructing MnOx-CeO 2 catalysts with controlled dispersion and interface properties, the significant promotion effect of interfacial contact between CeO 2 and crystalline Mn 3 O 4 in NH 3 -SCR was revealed. Although dispersed MnOx exhibited the combined merits of strong interaction with CeO 2 , improved textural property and abundant adsorption sites for NO/NH 3 , the catalytic performance was still not superior. With advent of Mn 3 O 4 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 Mn 3 O 4 occurred, emphasizing the importance of Mn 3 O 4 /CeO 2 boundary. Further mechanism analyses from in situ NH 3 -DRIFTS, quantitative titration of surface NOx with NH 3 and kinetics measurement disclosed the crucial role of crystalline Mn 3 O 4 in activating NH 3 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 NH 3 -SCR. [ABSTRACT FROM AUTHOR]