CeO2 - CuO_x Interactions and the Controlled Assembly of CeO2(111) and CeO2(100) Nanoparticles on an Oxidized Cu(111) Substrate

摘要

The catalytic performance of ceria-based heterogeneous catalysts in many chemical transformations (water—gas shift reaction, CO oxidation, alcohol synthesis from CO/CO2 hydrogenation, etc.) is affected by the surface structure of the ceria. To control the performance of ceria-containing inverse catalysts, we devised a method to grow ceria nanoparticles (NPs) exposing exclusively either (111) or (100) surfaces and characterized their surface structures by scanning tunneling microscopy. When cerium is yapor-deposited on Cu(111) in a background of molecular O2, only CeO2(111) NPs grow. However, if the surface of Cu(111) is preoxidized with O2 or NO2 to form a rectangular copper oxide phase, probably Cu4O3(001), CeO2(100) NPs grow on the oxide template instead. These experimental findings are interpreted using results of density functional calculations. The (100) surface of bulk ceria reconstructs to preserve charge neutrality. This is not necessary for CeO2(100) NPs grown on Cu4O3(001), where the topmost oxygen layer of Cu4O3 is shared with the interfacial layer of cerium. After the CeO2(100)/CuO_x/Cu(111) surfaces were exposed to CO, the copper oxide was reduced but the shape of the CeO2(100) NPs remained intact. This opens the door for diverse applications in catalysis.