Single-crystalline α-MnO2 catalysts with tailored exposed crystal facets for boosting catalytic soot oxidation: The crystal facet-dependent activity

Abstract

The distribution and coordination states of surface oxygen and metal ions in pure-phase metal oxides are dominated by the exposed crystal facets, which directly affects its physicochemical properties. Herein, we have elaborately constructed three catalysts of single-crystalline α-MnO2 nanowires with predominantly exposed {310}, {110} and {100} facets, respectively. The α-MnO2 catalyst exhibits a strong facet-dependent catalytic activity for the three-phase reaction of catalytic soot oxidation. Compared with the low-index {110} and {100} facets, the α-MnO2 catalyst with exposed high-index {310} facet exhibits the highest catalytic activities (T50 = 333 °C, TOF = 1.127 h−1), the lowest apparent activation energy (68.4 KJ mol−1), and excellent catalytic stability during soot oxidation. Combining the results of characterizations and density functional theory (DFT) calculations, the intrinsic mechanism of crystal facet-dependent catalytic activity for soot oxidation is revealed: The selectively exposed α-MnO2{310} facets can induce the formation of coordinative unsaturated atoms and surface defect sites, enhancing the adsorption-activation ability for O2 and NO. In-depth understanding of the face-dependent catalytic activity of α-MnO2 catalyst is valuable for the acquisition of high-efficient non-precious metal catalysts during soot oxidation.