Redox dynamics and surface structures of an active palladium catalyst during methane oxidation

Area of Science:

• Heterogeneous catalysis
• Materials science
• Surface chemistry

Background:

• Palladium (Pd) catalysts are highly effective for complete methane oxidation.
• The precise nature of active species and dynamic structural changes in Pd catalysts remain incompletely understood.
• Understanding these dynamics is crucial for optimizing methane oxidation processes.

Purpose of the Study:

• To investigate the active state and catalytic function of palladium nanoparticles (NPs) during methane oxidation.
• To elucidate the structural dynamics and phase composition of Pd NPs under reaction conditions.
• To correlate observed phenomena with catalytic activity using theoretical calculations.

Main Methods:

• Operando transmission electron microscopy (TEM) for real-time structural analysis.
• Near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) for surface electronic state determination.
• Density functional theory (DFT) calculations for mechanistic insights.
• Simultaneous mass spectrometry (MS) for reaction product analysis.

Main Results:

• Palladium nanoparticle size, phase composition, and dynamics are sensitive to gas-phase chemical potential.
• The catalytically active state involves phase coexistence and oscillatory transitions between Pd and palladium oxide (PdO).
• DFT calculations support the observed redox dynamics and identify strained PdO as energetically favorable for methane oxidation.

Conclusions:

• Catalytic activity in methane oxidation over Pd NPs is linked to dynamic interplay between coexisting Pd and PdO phases.
• Oscillatory phase transitions are a key feature of the active catalytic state.
• Strained PdO exhibits enhanced energetics, contributing significantly to the overall catalytic performance.