Redox Dynamics and Surface Structures of an Active Palladium Catalyst during Methane Oxidation

Abstract

Abstract Catalysts based on palladium are among the most effective in the complete oxidation of methane. Despite extensive studies, the nature of their catalytically active species and conceivable structural dynamics remains elusive. Here, we combine operando transmission electron microscopy (TEM) with near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and density functional theory (DFT) calculations to investigate the active state and catalytic function of Pd nanoparticles (NPs) under methane oxidation conditions. By direct imaging we show how the particle size, phase composition and dynamics respond to changes of the gas-phase chemical potential and how Pd catalysts transform from a static state to a highly dynamic, catalytically active state that is characterized by phase coexistence and oscillatory phase transition in a reactive atmosphere. Aided by DFT calculations, we rationalize the origin for the observed redox dynamics and provide atomistic insights into the active structures and the underlying reaction mechanism.