Activating Molybdenum Carbide Nanoparticle Catalysts under Mild Conditions Using Thermally Labile Ligands.

Area of Science:

• Materials Science
• Catalysis
• Nanotechnology

Background:

• Transition-metal carbides exhibit noble-metal-like properties, making them attractive for catalysis.
• Nanostructuring transition-metal carbides enhances their catalytic activity due to increased surface area.
• Removing long-chain ligands from nanoparticle surfaces is crucial for accessing active sites but often requires high temperatures.

Purpose of the Study:

• To develop a low-temperature method for removing surface ligands from colloidal α-MoC_1- nanoparticles.
• To replace oleylamine ligands with thermally labile tert-butylamine ligands for easier removal.
• To investigate the impact of ligand exchange on catalytic activity and site accessibility.

Main Methods:

• Ligand exchange reaction using tert-butylamine.
• Characterization by solution ¹H NMR, FT-IR, and TGA-MS.
• Catalytic site density determination via CO chemisorption.
• Evaluation of CO₂ hydrogenation reaction performance.

Main Results:

• Successfully exchanged 60% of oleylamine ligands with tert-butylamine.
• Mild thermal treatment at 250 °C removed tert-butylamine ligands, activating ~25% of binding sites.
• Ligand-exchanged nanoparticles showed accessible active sites after low-temperature treatment, unlike native nanoparticles.
• Distinct differences in catalytic activity and selectivity were observed in CO₂ hydrogenation.

Conclusions:

• Thermally labile ligand exchange offers a viable strategy for low-temperature activation of transition-metal carbide catalysts.
• This approach enhances the accessibility of catalytic sites without compromising catalyst integrity through high-temperature annealing.
• The modified α-MoC_1- nanoparticles demonstrate improved catalytic performance in CO₂ hydrogenation.