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Exploring the Radical Nature of a Carbon Surface by Electron Paramagnetic Resonance and a Calibrated Gas Flow

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Time-resolved surface reaction kinetics in the pressure gap.

Tzu-En Chien¹, Lea Hohmann¹, Dan J Harding¹

¹Department of Chemical Engineering, KTH Royal Institute of Technology, Stockholm 100 44, Sweden. djha@kth.se.

Faraday Discussions

|May 17, 2024

Summary

Near-Ambient Pressure Velocity Map Imaging (NAP-VMI) directly measures CO oxidation kinetics on Pd(110). A specific oxide structure is highly active, but CO2 production is suppressed at higher oxygen pressures.

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Area of Science:

Surface Science
Chemical Kinetics
Catalysis

Background:

Studying catalytic reactions in the pressure gap is challenging.
Existing methods have limitations in resolving reaction dynamics.

Purpose of the Study:

To extend the Near-Ambient Pressure Velocity Map Imaging (NAP-VMI) technique for studying catalytic reaction kinetics.
To investigate the CO oxidation reaction on the Pd(110) surface at near-ambient pressures.

Main Methods:

Utilized NAP-VMI combined with molecular beam surface scattering.
Measured time- and velocity-resolved kinetics of CO scattering and oxidation on Pd(110).
Investigated reactions at oxygen pressures up to 1 × 10^-5 mbar.

Main Results:

Identified a highly active c(2 × 4) oxide structure at low O2 pressure.
Observed two reaction channels for CO2 product formation, linked to distinct CO binding sites.
Determined an effective CO oxidation activation energy of 1.0 ± 0.13 eV.
Found CO2 production is suppressed at higher O2 pressures due to surface structure changes.

Conclusions:

The c(2 × 4) oxide structure on Pd(110) is crucial for active CO oxidation.
Surface O-atom coverage and structure influence CO surface lifetime and catalytic activity.
NAP-VMI is a powerful tool for probing reaction dynamics in the pressure gap.