Intrinsic Ligand Effect Governing the Catalytic Activity of Pd Oxide Thin Films

Abstract

High-pressure X-ray photoelectron spectroscopy, mass spectrometry, and density functional theory calculations have been combined to study methane oxidation over Pd(100). The measurements reveal a high activity when a two-layer PdO(101) oriented film is formed. Although a one-layer PdO(101) film exhibits a similar surface structure, no or very little activity is observed. The calculations show that the presence of an oxygen atom directly below the coordinatively unsaturated Pd atom in the two-layer PdO(101) film is crucial for efficient methane dissociation, demonstrating a ligand effect that may be broadly important in determining the catalytic properties of oxide thin films.

Evolution of self-sustained kinetic oscillations in the catalytic oxidation of propane over a nickel foil

“…Indeed, it is considered that late transition metal oxides such as RuO 2 , PdO, and IrO 2 are more active in the catalytic oxidation of CO and hydrocarbons than corresponding metals [63]. For example, Martin et al [64] studied the oxidation of methane on Pd(100) and showed that the high activity was achieved when a two-layer oriented film of PdO(101) was formed on the palladium surface. Using DFT calculations, they showed that the presence of oxygen atoms directly below coordinatively unsaturated (cus) palladium atoms in the two-layer oxide film is crucial for efficient dissociation of methane.…”

Highly Active and Stable CH4 Oxidation by Substitution of Ce4+ by Two Pd2+ Ions in CeO2(111)

“…1,7−9 In automotive three-way catalysis, Pd is already extensively used to catalyze hydrocarbon oxidation. 10−13 The function of CeO 2 in these catalysts is mainly to store and release oxygen, while more recently its ability to maintain a high dispersion of transition metals has been emphasized. 14−16 Although the importance of a close interaction between Pd and CeO 2 in catalytic oxidation chemistry has been clearly demonstrated, 1,3,7,17 the exact structure of the active Pd species remains unclear.…”

Catalytic Oxidation of Methane: Pd and Beyond

“…The active phase of Pd during methane oxidation is a long‐standing puzzle, but both experimental evidences and fundamental studies indicate that PdO is the most active phase for methane oxidation. Significant advances have been made over the last decade in understanding alkane activation and oxidation on well‐defined PdO(101) surfaces via a combination of molecular simulations, ultra‐high vacuum (UHV) and in situ measurements . DFT calculations, high‐pressure X‐ray photoelectron spectroscopy and mass spectrometry results for methane oxidation performed over a range of Pd and PdOx surfaces revealed that under‐coordinated Pd sites in PdO(101) are the most active, provided that at least a second layer of oxide is present .…”