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Bridging the pressure and materials gaps: high pressure sum frequency generation study on supported Pd nanoparticles
Dellwig1, Rupprechter, Unterhalt
1Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany.
Physical Review Letters
|September 16, 2000
Summary
Infrared-visible sum frequency generation spectroscopy reveals CO adsorption sites on palladium nanoparticles. Gas pressure primarily dictates site occupancy, with particle structure and temperature having minor effects.
Area of Science:
- Surface science
- Nanoparticle catalysis
- Vibrational spectroscopy
Background:
- Palladium nanoparticles are crucial catalysts.
- Understanding CO adsorption on Pd is vital for catalysis.
- Sum frequency generation (SFG) spectroscopy is a powerful surface-sensitive technique.
Purpose of the Study:
- To investigate CO stretching vibrations on alumina-supported Pd nanoparticles using SFG.
- To determine the influence of pressure, particle size, and temperature on CO adsorption.
- To identify CO adsorption sites on Pd nanocrystals.
Main Methods:
- Infrared-visible sum frequency generation (SFG) vibrational spectroscopy.
- In situ measurements across a wide pressure range (10^-7 to 200 mbar).
- Analysis of Pd nanoparticles with 3 and 6 nm mean sizes supported on alumina.
Main Results:
- SFG successfully monitored CO stretching vibrations on Pd nanoparticles.
- Two distinct adsorption sites (twofold bridging and on-top) were identified.
- CO adsorption site occupancy is predominantly controlled by gas phase pressure.
- Particle structure and temperature showed a lesser influence on adsorption.
Conclusions:
- SFG is effective for studying CO adsorption dynamics on supported nanoparticles.
- Gas pressure is the key factor governing CO adsorption site preference on Pd nanocrystals.
- Surface defects play a significant role in the adsorption behavior of Pd aggregates.