Stability and Temperature-Induced Agglomeration of Rh Nanoparticles Supported by CeO2

Area of Science:

• Catalysis Science
• Materials Science
• Surface Chemistry

Background:

• Understanding metal-support interactions is crucial for catalyst design.
• Rhodium (Rh) on ceria (CeO2) is a significant catalytic system.
• Controlling nanoparticle size and dispersion impacts catalytic activity.

Purpose of the Study:

• To investigate the impact of reduction and heat treatment on Rh particle size on CeO2.
• To elucidate the role of ceria's mobile oxygen species in Rh particle evolution.
• To explore redispersion mechanisms of sintered Rh nanoparticles.

Main Methods:

• X-ray photoelectron spectroscopy (XPS) for surface composition and oxidation states.
• High-resolution transmission electron microscopy (HRTEM) for particle size and morphology.
• Diffuse reflectance infrared spectroscopy (DRIFTS) after CO adsorption to probe surface species.

Main Results:

• Low-temperature reduction (373-423 K) maintained small Rh particle sizes (avg. 2.3 ± 1.1 nm) without agglomeration.
• Heating to 773 K induced significant Rh particle sintering, particularly for well-dispersed particles.
• Mobile ceria oxygens were found to dictate the oxidation state of Rh and facilitate reoxidation and redispersion upon heating.

Conclusions:

• Low-temperature reduction is effective for preserving small Rh nanoparticles on CeO2.
• Sintering is favored at high temperatures, but reoxidation can promote Rh redispersion via Rh-O-Ce bond formation.
• The dynamic nature of ceria's oxygen sublattice plays a key role in the stability and behavior of supported Rh catalysts.