Nonthermalized Precursor-Mediated Dissociative Chemisorption at High Catalysis Temperatures

Area of Science:

• Surface science
• Chemical kinetics
• Heterogeneous catalysis

Background:

• Understanding methane (CH4) chemisorption on metal surfaces is crucial for catalysis.
• C-H bond activation is a key step in many catalytic processes, including methane conversion.
• Previous studies often assumed thermal equilibrium between molecules and the surface.

Purpose of the Study:

• To elucidate the mechanism of methane chemisorption and C-H bond activation on Ir(111).
• To investigate the role of molecular vibrational excitation and surface atom dynamics.
• To explore the impact of surface temperature on reaction probability.

Main Methods:

• Quasiclassical trajectory (QCT) calculations.
• Vibrational-state-selected molecular beam-surface scattering experiments.
• Analysis of surface atom displacement and transition-state geometries.

Main Results:

• A nonthermal, hot-molecule mechanism for C-H bond activation was identified.
• Low-energy vibrationally excited CH4 molecules react in the physisorption well before energy accommodation.
• Reaction probability strongly depends on surface temperature due to the role of Ir atom thermal motion.
• Surface atom displacements create transient low-barrier reaction sites.

Conclusions:

• Methane activation on Ir(111) proceeds via a mechanism driven by molecular excitation and dynamic surface atom motion.
• Surface defects, specifically transient atom displacements, play a significant role in high-temperature heterogeneous catalysis.
• This work offers a new perspective on how surface dynamics influence catalytic reactivity.