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Iridium nanocrystal synthesis and surface coating-dependent catalytic activity
Cynthia A Stowell1, Brian A Korgel
1Department of Chemical Engineering, Texas Materials Institute and Center for Nano and Molecular Science and Technology, The University of Texas, Austin, Texas 78712-1062, USA.
Nano Letters
|September 24, 2005
Summary
Iridium nanocrystal synthesis yielded varying catalytic activity based on capping ligands. Tetraoctylphosphonium bromide (TOPB)-coated iridium nanocrystals showed the highest hydrogenation activity, which improved with recycling but eventually decreased due to ligand desorption.
Area of Science:
- Materials Science
- Nanotechnology
- Catalysis
Background:
- Iridium (Ir) nanocrystals are valuable in catalysis.
- Controlling nanocrystal surface properties is crucial for catalytic performance.
- Ligand choice significantly impacts nanocrystal synthesis and reactivity.
Purpose of the Study:
- To synthesize iridium nanocrystals using different capping ligands.
- To evaluate the catalytic activity of these nanocrystals in 1-decene hydrogenation.
- To understand the role of capping ligands in iridium nanocrystal catalysis.
Main Methods:
- Synthesis of Ir nanocrystals via reduction of a precursor with hexadecanediol.
- Employing four distinct capping ligand systems: oleic acid/oleylamine, trioctylphosphine (TOP), tetraoctylammonium bromide (TOAB), and tetraoctylphosphonium bromide (TOPB).
- Assessing nanocrystal quality (size/shape distribution) and catalytic performance in 1-decene hydrogenation.
Main Results:
- Oleic acid/oleylamine-capped Ir nanocrystals exhibited the highest quality with narrowest size and shape distribution.
- Oleic acid/oleylamine and TOP-capped nanocrystals were catalytically inactive.
- TOAB and TOPB-coated nanocrystals catalyzed 1-decene hydrogenation, with TOPB showing superior turnover frequencies.
- Catalytic activity increased with recycling due to ligand desorption, but excessive desorption led to precipitation and reduced activity.
Conclusions:
- The choice of capping ligand is critical for the catalytic activity of iridium nanocrystals.
- TOPB is an effective ligand for creating active iridium hydrogenation catalysts.
- Ligand management is essential for optimizing and maintaining nanocatalyst performance over time.