Spatially Nonuniform Reaction Rates during Selective Oxidation on Gold

Area of Science:

• Surface Science
• Heterogeneous Catalysis
• Nanoscale Chemistry

Background:

• Understanding the reactivity of adsorbed oxygen on metal surfaces is crucial for designing efficient catalytic processes.
• The selective oxidation of methanol is a key reaction in producing valuable chemicals and fuels.
• Gold surfaces, particularly Au(110)-(1×2), exhibit complex reactivity influenced by surface structure.

Purpose of the Study:

• To investigate the role of adsorbed oxygen's mesoscale structure in the selective oxidation of methanol on Au(110)-(1×2).
• To elucidate the relationship between surface structure, oxygen coverage, and reaction kinetics.
• To explore the generality of structure-dependent reactivity using 2-propanol as a co-reactant.

Main Methods:

• In situ scanning tunneling microscopy (STM) was employed to visualize and analyze the surface structure and oxygen distribution.
• Kinetic measurements were performed to correlate surface morphology with reaction rates.
• Varying oxygen coverages were used to probe the influence of initial conditions on reactivity.

Main Results:

• Nonuniform oxygen reactivity was observed, with preferential oxygen consumption along the [11̅0] direction at coverages above 0.06 ML.
• Directionally specific reactivity is linked to weaker oxygen binding at chain termini and strain release.
• A sudden increase in reactivity for methanol oxidation occurs below ~0.06 ML oxygen coverage due to island destabilization.
• Analogous, but kinetically different, behavior was observed for 2-propanol oxidation, highlighting the phenomenon's generality.

Conclusions:

• Both atomic and mesoscale surface structures significantly influence the kinetics of selective oxidation reactions.
• The arrangement and stability of adsorbed oxygen islands play a critical role in determining reaction pathways and rates.
• These findings provide fundamental insights into structure-sensitive catalysis on gold surfaces.