Thermal evolution of cobalt deposits on Co3O4(111): atomically dispersed cobalt, two-dimensional CoO islands, and metallic Co nanoparticles

• Published in: Physical chemistry chemical physics : PCCP 2015-09, Vol.17 (36), p.23538-23546
• Main Authors: Mehl, S, Ferstl, P, Schuler, M, Toghan, A, Brummel, O, Hammer, L, Schneider, M. A, Libuda, J
• Format: Article
• Language: English
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c5cp03922c

Cobalt oxide nanomaterials show high activity in several catalytic reactions thereby offering the potential to replace noble metals in some applications. We have developed a well-defined model system for partially reduced cobalt oxide materials aiming at a molecular level understanding of cobalt-oxide-based catalysis. Starting from a well-ordered Co 3 O 4 (111) film on Ir(100), we modified the surface by deposition of metallic cobalt. Growth, structure, and adsorption properties of the cobalt-modified surface were investigated by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and infrared reflection absorption spectroscopy (IRAS) using CO as a probe molecule. The deposition of a submonolayer of cobalt at 300 K leads to the formation of atomically dispersed cobalt ions distorting the surface layer of the Co 3 O 4 film. Upon annealing to 500 K the Co ions are incorporated into the surface layer forming ordered two-dimensional CoO islands on the Co 3 O 4 grains. At 700 K, Co ions diffuse from the CoO islands into the bulk and the ordered Co 3 O 4 (111) surface is restored. Deposition of larger amounts of Co at 300 K leads to formation of metallic Co aggregates on the dispersed cobalt phase. The metallic particles sinter at 500 K and diffuse into the bulk at 700 K. Depending on the degree of bulk reduction, extended Co 3 O 4 grains switch to the CoO(111) structure. All above structures show characteristic CO adsorption behavior and can therefore be identified by IR spectroscopy of adsorbed CO. Cobalt deposition onto Co 3 O 4 (111) leads to formation of atomically dispersed cobalt species, which form ordered two-dimensional oxide islands upon annealing.