Carbon monoxide-induced adatom sintering in a Pd-Fe3O4 model catalyst.

Area of Science:

• Surface science
• Catalysis
• Materials science

Background:

• Metal cluster coarsening is a critical factor in catalyst deactivation.
• The influence of gas molecules on metal adatom mobility and cluster formation is complex and system-dependent.

Purpose of the Study:

• To elucidate the role of carbon monoxide (CO) in the mobility and coalescence of palladium (Pd) adatoms on a Fe3O4(001) surface.
• To identify the specific species responsible for gas-induced mass transport.
• To investigate the counteracting effect of surface hydroxyls on Pd adatom behavior.

Main Methods:

• Utilizing scanning tunneling microscopy (STM) to observe the dynamic evolution of Pd adatoms at room temperature.
• Atom-by-atom tracking of adatom behavior from dispersed states to cluster formation.

Main Results:

• Pd-carbonyl species were identified as the primary drivers of Pd adatom mobility on the Fe3O4(001) surface.
• Cluster nucleation and subsequent coarsening via diffusion and coalescence were observed once a critical density of mobile Pd species was reached.
• Surface hydroxyl groups were found to impede Pd mobility by preventing carbonyl formation, leading to isolated Pd atoms.

Conclusions:

• The study identifies Pd-carbonyl formation as the key mechanism for CO-induced mass transport and cluster coarsening in the Pd/Fe3O4 system.
• Surface functional groups, such as hydroxyls, can significantly alter metal adatom mobility and aggregation behavior.
• Understanding these gas-surface interactions is crucial for controlling catalyst nanostructure and performance.