Ab initio thermodynamic evaluation of Pd atom interaction with CeO(2) surfaces

Area of Science:

• Materials Science
• Surface Chemistry
• Catalysis

Background:

• Palladium supported on ceria is a key catalytic material for automotive three-way catalysis, catalytic combustion, and solid-oxide fuel cell (SOFC) anodes.
• Catalytic activity is sensitive to the morphology, oxidation state, and particle size of palladium on ceria, which depend on experimental conditions.

Purpose of the Study:

• To investigate the thermodynamic stability of palladium atoms, oxides, and small particles on different ceria crystal surfaces using ab initio calculations.
• To understand how operating conditions like temperature, oxygen pressure, and cell potential affect the stability of palladium on ceria.

Main Methods:

• Employed ab initio thermodynamics based on density functional theory (DFT+U) methods.
• Evaluated the stability of various palladium species (atoms, PdO(x), small particles) on CeO(2) (111), (110), and (100) surfaces.

Main Results:

• Palladium incorporation into the ceria surface to form a mixed oxide is thermodynamically favorable under specific oxygen partial pressure and temperature ranges.
• Palladium can incorporate into ceria lattice sites, exhibiting a Pd(4+) oxidation state on the CeO(2) (111) surface.
• The ceria support alters the transition points between palladium oxidation states (Pd(0), Pd(2+), Pd(4+)) compared to bulk palladium, stabilizing oxidized forms.

Conclusions:

• The study provides insights into the structural stability of palladium on ceria surfaces under catalytic operating conditions.
• Temperature, oxygen pressure, and SOFC cell potential are identified as critical factors influencing the stable states of supported palladium.