Crystal facets usually play an important role in the catalytic activity of inorganic single crystals. In this work, two alpha-Mn2O3 single crystals with an octahedron (exposed with (1 1 1) facet) and a truncated octahedron (exposed with both (1 1 1) and (0 01) facets) were successfully prepared by a simple solvent thermal reaction, and their catalytic activities were evaluated by the selective catalytic reduction (SCR) of NOx with NH3. The results show that the catalytic performance of the alpha-Mn2O3 single crystal with a truncated octahedron was enhanced in comparison with the alpha-Mn2O3 single crystal with an octahedron by the exposure of a small fraction of (0 01) facets. This can be attributed to the new active sites created by charge redistribution on the surface of the (0 0 1) facets, which provides more adsorption sites, facilitating the further adsorption and reaction of NH3 and NO molecules, and thereby enhancing the catalytic performance. This work should provide new insight into the understanding of crystal-facet-dependent reactivity and important guides for the design and preparation of SCR catalysts with high activity. (C) 2018 Elsevier Inc. All rights reserved.