Crystal-Plane-Controlled Surface Chemistry and Catalytic Performance of Surfactant-Free Cu2O Nanocrystals

Surfactant-free Cu2O nanocrystals, including cubes exposing {100} crystal planes, octahedra exposing {111} crystal planes, and rhombic dodecahedra exposing {110} crystal planes, were used as model catalysts to study the effect of the crystal plane on the surface chemistry and catalytic performance for CO oxidation of Cu2O nanocrystals. The catalytic performance follows the order of octahedra >> rhombic dodecahedra>cubes; this suggests that Cu2O(111) is most active in catalyzing CO oxidation among Cu2O (111), (110), and (100) surfaces. CO temperature-programmed reduction results demonstrate that Cu2O octahedra are the most easily reduced of the Cu2O cubes, octahedra, and rhombic dodecahedra. Diffuse reflectance FTIR spectra show that CO chemisorption on Cu2O nanocrystals depends on their shape and the chemisorption temperature. CO chemisorption is strongest on rhombic dodecahedra at 30 degrees C, but at 150 degrees C on octahedra. Both the reducibility and chemisorption ability of various Cu2O nanocrystals toward CO are consistent with their catalytic performance in CO oxidation. The observed surface chemistry and catalytic performance in CO oxidation of various Cu2O nanocrystals can be well correlated with their exposed crystal plane and surface composition/structure. Cu2O octahedra expose the {111} crystal plane with coordinated, unsaturated Cu-I sites, and thus, are most active in chemisorbing CO and catalyzing CO oxidation. These results nicely demonstrate the crystal-plane-controlled surface chemistry and catalytic performance of oxide catalysts.