Direct evidence of atomic-scale structural fluctuations in catalyst nanoparticles

Area of Science:

• Materials Science
• Chemical Engineering
• Nanotechnology

Background:

• Rational catalyst design necessitates a deep mechanistic understanding of catalytic processes at the atomic scale.
• Heterogeneous catalysts typically function by adsorbing reactants on their surface, facilitating bond dissociation and formation for product synthesis.

Purpose of the Study:

• To investigate the mechanistic pathways in catalytic processes, using single-walled carbon nanotube (SWCNT) growth as a model system.
• To explore the role of dynamic phase transformations within catalyst particles during SWCNT growth.

Main Methods:

• In situ atomic-resolution imaging using an environmental transmission electron microscope (ETEM) to observe Cobalt catalyst nanoparticles.
• Automated atomic-scale structural analysis of time-resolved ETEM images to quantify catalyst carbon content fluctuations.
• Reactive molecular dynamics (RMD) simulations to model carbon atom distribution and evolution within the catalyst particle.

Main Results:

• Observed dynamic phase transformations within Cobalt catalyst nanoparticles during SWCNT growth.
• Quantified fluctuations in catalyst carbon content, correlating them with SWCNT growth rates.
• Found complementary fluctuations between catalyst carbon concentration and nanotube growth rates.

Conclusions:

• Catalytic pathways can involve internal catalyst particle dynamics, including the formation and decomposition of metastable phases.
• The developed approach combining real-time imaging and molecular dynamics simulations aids in understanding and designing catalysts.
• This methodology can improve reaction efficiencies and selectivity for desired nanostructure growth.