CO dissociation on iron nanoparticles: size and geometry effects

Area of Science:

• Computational materials science
• Surface chemistry
• Nanotechnology

Background:

• Iron nanoparticles are crucial catalysts in various chemical processes, including carbon nanotube synthesis.
• Understanding the reactivity of iron nanoparticles is essential for optimizing catalytic applications.
• Previous studies often simplified nanoparticle morphology, potentially misrepresenting catalytic behavior.

Purpose of the Study:

• To systematically investigate the CO dissociation reactivity of iron nanoparticles (0.5-1.4 nm) and bulk surfaces.
• To explore the impact of particle size, morphology (symmetric vs. rugged), and local structure on activation energies and reaction rates.
• To determine the reliability of small nanoparticles and bulk surfaces as models for larger iron nanoparticle catalysis.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to model iron nanoparticles and bulk surfaces.
• Activation energies for Carbon Monoxide (CO) dissociation were computed for various nanoparticle sizes and geometries.
• Reaction rates were calculated under conditions relevant to gas-phase chemical vapor deposition (CVD).

Main Results:

• Activation energies for CO dissociation ranged from 1.1 to 2.1 eV, decreasing with increasing particle size and roughness.
• Local particle morphology significantly impacted activation energies, with variations up to 0.9 eV on a single particle.
• Reaction rates varied over five orders of magnitude, highlighting the sensitivity to nanoparticle characteristics.
• Smallest particles and bulk surfaces are unreliable models for catalysis on larger iron nanoparticles.
• Predictive d-band and linear-energy relationships were found unsuitable due to varying reaction mechanisms.

Conclusions:

• The reactivity of iron nanoparticles for CO dissociation is highly dependent on size, geometry, and local morphology.
• Reaction mechanisms and Fe-Fe bond lengths dictate CO dissociation, influencing back-bonding interactions.
• CO dissociation on nano-iron is more complex than on traditional noble metal catalysts, necessitating detailed structural considerations.