On the surface-dependent oxidation of Cu2O during CO oxidation: Cu2+ is more active than Cu+
Yanan Gao, Long Zhang, Arno J. F. van Hoof, Emiel J. M. Hensen
Abstract
Solid materials can exhibit very different surface catalytic properties depending on the exposed surface. Different from the previous finding by Bao et al. ( Angew. Chem. Int. Ed. 50 (2011) 12294–12298 ) that Cu 2 O octahedra are more active than Cu 2 O cubes in CO oxidation, we found that Cu 2 O cubes exposing {100} surface showed significantly higher activity than Cu 2 O octahedra exposing {111} surface in the reaction. The Cu 2 O(100) surface was found to be oxidized during CO oxidation, leading to the formation of a CuO surface layer. On the other hand, Cu 2 O(111) strongly resisted such surface oxidation under CO oxidation conditions. Density functional theory calculations demonstrate that CO oxidation follows a Mars-Van Krevelen mechanism on Cu 2 O(111) with a high activation barrier of 1.36 eV. In contrast, the overall activation barrier is only 0.58 eV for CuO(111). These differences explain well the higher activity of oxidized Cu 2 O cubes.