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Segregation Phenomena in Size-Selected Bimetallic CuNi Nanoparticle Catalysts
Lukas Pielsticker1, Ioannis Zegkinoglou1, Nuria J Divins1
1Department of Physics, Ruhr University Bochum , 44780 Bochum, Germany.
The Journal of Physical Chemistry. B
|October 26, 2017
Summary
Nickel segregates to copper-nickel nanoparticle surfaces at high temperatures, driven by pretreatment and gas environments, not just surface energy. These bimetallic nanoparticles show remarkable stability against sintering up to 700°C.
Area of Science:
- Materials Science
- Surface Science
- Nanotechnology
Background:
- Bimetallic nanoparticles (NPs) are crucial for catalysis.
- Understanding surface segregation and restructuring is key to controlling NP behavior.
- Copper-nickel (Cu-Ni) alloy NPs offer tunable properties for various applications.
Purpose of the Study:
- To investigate surface segregation, restructuring, and sintering in Cu-Ni NPs.
- To determine the influence of temperature, chemical state, and gas environment on NP behavior.
- To elucidate the driving forces behind segregation and alloy formation in bimetallic NPs.
Main Methods:
- Near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and ultrahigh vacuum XPS.
- Operando analysis of NP composition under CO2 hydrogenation.
- Atomic force microscopy (AFM) for sintering studies.
Main Results:
- Nickel segregation to NP surfaces observed at elevated temperatures in reactive atmospheres (O2, H2).
- NP pretreatment, gas environment, and oxide formation energy are primary drivers of segregation, overriding surface free energy.
- High stability against sintering up to 700 °C confirmed by AFM.
- Nickel oxides exhibit high stability, and high valence states are crucial for segregation.
Conclusions:
- Surface segregation in Cu-Ni NPs is complex, influenced by multiple factors beyond surface energy.
- Results offer new strategies for tuning nanocatalyst surface composition via plasma and annealing.
- Findings provide insights into bimetallic NP behavior, differing from bulk counterparts.
