Size-dependent self-limiting oxidation of free palladium clusters

Area of Science:

• Physical Chemistry
• Surface Science
• Computational Chemistry

Background:

• Palladium clusters are crucial in catalysis.
• Understanding their oxidation behavior is key to controlling catalytic activity.
• Size-dependent reactivity is a common phenomenon in nanomaterials.

Purpose of the Study:

• Investigate the size-dependent reactivity of small palladium clusters (Pd(x)(+), x=2-7) with molecular oxygen.
• Elucidate the structural and bonding aspects governing oxygen chemisorption on palladium clusters.
• Identify factors contributing to the stability of oxidized palladium cluster products.

Main Methods:

• Gas phase ion trap experiments under multicollision conditions.
• Temperature-dependent reactivity studies.
• First-principles density functional theory (DFT) simulations.
• Studies on pre-oxidized palladium clusters (Pd(x)O(+) and Pd(x)O2(+)).

Main Results:

• Reactivity of Pd(x)(+) with O2 is strongly size-dependent.
• Pd(x)O4(+) complexes exhibit significant stability and resistance to further oxidation.
• DFT simulations reveal a dissociatively chemisorbed bridging oxygen structure responsible for Pd(x)O4(+) stability.
• This structure impedes further oxygen chemisorption; molecular O2 physisorption occurs only at cryogenic temperatures.

Conclusions:

• The specific bridging oxygen atomic structure on Pd(x)O4(+) dictates its stability.
• Size-dependent chemisorption and a stable oxidation state of Pd(x)O4(+) are key findings.
• Experimental and computational methods provide complementary insights into palladium-oxygen interactions.