The actual Co(10-12) surface structure and CO activation.

Area of Science:

• Surface Science
• Catalysis
• Materials Science

Background:

• The hexagonal close-packed cobalt (Co) (10-12) surface exhibits two known atomic arrangements.
• Previous studies predominantly utilized the Co(10-12)-A termination, identified via low-energy electron diffraction (LEED).
• Subsurface oxygen species (O_sub) can persist on Co(10-12) surfaces, complicating characterization and reactivity studies.

Purpose of the Study:

• To investigate the influence of subsurface oxygen on the Co(10-12) surface.
• To prepare a clean Co(10-12) surface free from subsurface oxygen.
• To characterize the atomic arrangement and catalytic activity of the oxygen-free Co(10-12) surface.

Main Methods:

• Utilized a novel strategy involving H₂-induced segregation of subsurface oxygen.
• Employed ion sputtering and annealing to remove segregated oxygen, preparing a clean surface.
• Characterized the surface termination and coordination using low-energy electron diffraction (LEED) intensity/voltage analysis.

Main Results:

• Successfully prepared an oxygen-free Co(10-12) surface exhibiting the Co(10-12)-B termination.
• The Co(10-12)-B termination features sevenfold, ninefold, and tenfold coordinated cobalt atoms.
• Direct CO activation is significantly favored over H-assisted CO activation on the Co(10-12)-B surface, contrasting with the Co(10-12)-A surface.

Conclusions:

• The Co(10-12)-B termination represents a previously overlooked surface structure for cobalt.
• The catalytic behavior, specifically CO activation, on the Co(10-12)-B surface differs markedly from the Co(10-12)-A surface.
• Fundamental understanding of Fischer-Tropsch synthesis on cobalt catalysts requires re-evaluation using the Co(10-12)-B surface.