Identifying site-dependent reactivity in oxidation reactions on single Pt particles

Area of Science:

• Heterogeneous catalysis
• Nanoparticle surface chemistry
• Surface science

Background:

• Catalytic nanoparticles exhibit heterogeneous surface sites influencing reactivity.
• Understanding nanoscale chemical information is crucial for directing nanoparticle reactivity.
• Site-specific reactivity on nanoparticles is influenced by surface properties and reaction conditions.

Purpose of the Study:

• To investigate reactivity variations across different surface sites of platinum (Pt) nanoparticles.
• To utilize hydroxyl-functionalized N-heterocyclic carbene (NHC) molecules as chemical markers.
• To detect site-dependent reactivity under varying oxidizing conditions (liquid and gas phases).

Main Methods:

• Anchoring NHC molecules onto Pt nanoparticle surfaces.
• Employing synchrotron-radiation-based infrared nanospectroscopy (IR) with 20 nm spatial resolution.
• Conducting complementary spatially averaged IR and X-ray spectroscopy (XAS) measurements.

Main Results:

• Identified enhanced reactivity at the periphery of Pt nanoparticles under both gas and liquid phase oxidizing conditions.
• Observed preferential oxidation of NHC hydroxyl groups to acid at the particle's perimeter under gas phase conditions.
• Detected NHC modification and reorientation (perpendicular to parallel) at the particle's periphery under liquid phase conditions, indicating aromatization via oxidative dehydrogenation.

Conclusions:

• Demonstrated higher reactivity of surface sites located at the nanoparticle periphery.
• Highlighted the significant influence of reaction conditions on site-dependent reactivity in catalytic nanoparticles.
• Provided nanoscale chemical insights into heterogeneous catalysis mechanisms.