Probing Active Sites on Pd/Pt Alloy Nanoparticles by CO Adsorption

Area of Science:

• Surface Science
• Materials Science
• Catalysis

Background:

• Palladium-platinum (Pd/Pt) alloy nanoparticles are crucial in catalysis.
• Understanding CO adsorption on these alloys is key to optimizing catalytic performance.
• Surface composition and atomic arrangement significantly influence adsorption properties.

Purpose of the Study:

• To investigate the adsorption behavior of carbon monoxide (CO) on Pd/Pt alloy nanoparticles with varying compositions.
• To elucidate the role of alloy composition and local atomic arrangement on CO adsorption sites and vibrational frequencies.
• To correlate experimental findings with theoretical calculations for a comprehensive understanding.

Main Methods:

• Preparation of PtPd alloy nanoparticles via physical vapor codeposition on α-Al2O3(0001) supports.
• Morphological and structural characterization using scanning electron microscopy (SEM) and grazing incidence X-ray diffraction (GIXRD).
• Polarization-dependent Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS) for CO adsorption studies.
• Density functional theory (DFT) calculations to determine the dependence of IR bands on local atomic arrangements.

Main Results:

• Well-defined, epitaxial Pd/Pt alloy nanoparticles were successfully synthesized.
• FT-IRRAS distinguished CO adsorption on different nanoparticle facets.
• The Pd/Pt alloy ratio significantly influenced CO adsorption frequencies.
• DFT calculations confirmed that local atomic arrangement and bulk composition affect IR band positions.
• Hydrogen adsorption was found to influence NP surface composition.

Conclusions:

• The study provides detailed insights into CO adsorption on Pd/Pt alloy nanoparticles.
• Both the overall alloy composition and the specific arrangement of neighboring atoms dictate CO adsorption behavior.
• This work contributes to the rational design of advanced catalytic materials.