The Structure of the Active Pd State During Catalytic Carbon Monoxide Oxidization.

Christopher M Goodwin,Anders Nilsson,Peter Amann,David Degerman,Uta Hejral,Stefano Albertin,Sara Blomberg,Edvin Lundgren,Mikhail Shipilin,Christoph Schlueter,Patrick Lömker,Hsin-Yi Wang

doi:10.1021/acs.jpclett.1c00620

Abstract

Using grazing incidence X-rays and X-ray photoelectron spectroscopy during the mass transfer limited catalytic oxidation of CO, the long-range surface structure of Pd(100) was investigated. Under the reaction conditions of 50:4 O2 to CO, 300 mbar pressure, and temperatures between 200 and 450 °C, the surface structure resulting from oxidation and the subsequent oxide reduction was elucidated. The reduction cycle was halted, and while under reaction conditions, angle-dependent X-ray photoelectron spectroscopy close to the critical angle of Pd and modeling of the data was performed. Two proposed models for the system were compared. The suggestion with the metallic islands formed on top of the oxide island was shown to be consistent with the data.

Highlights

Using grazing incidence X-rays and X-ray photoelectron spectroscopy during the mass transfer limited catalytic oxidation of CO, the long-range surface structure of Pd(100) was investigated
Pd(100) was used as a model catalyst to probe the structural rearrangement during CO oxidation approaching atmospheric pressures.[8−12] The surface structure is of particular interest in Pd due to the possibility of surface reconstructions and oxide formation during the catalytic reaction.[13]
Scanning tunneling microscopy (STM) studies have suggested morphologic changes during the catalysis, and gas-phase measurements have shown that oscillations of catalytic activity are possible.[17−19] The results of these studies indicate that the surface is dynamically changing under steady-state reaction conditions, and a more complex structure may appear as PdO becomes reduced

Summary

Introduction

Using grazing incidence X-rays and X-ray photoelectron spectroscopy during the mass transfer limited catalytic oxidation of CO, the long-range surface structure of Pd(100) was investigated. Scanning tunneling microscopy (STM) studies have suggested morphologic changes during the catalysis, and gas-phase measurements have shown that oscillations of catalytic activity are possible.[17−19] The results of these studies indicate that the surface is dynamically changing under steady-state reaction conditions, and a more complex structure may appear as PdO becomes reduced. The dynamic nature of Pd(100) has limited surface morphology and chemical studies during reaction conditions to UHV or low pressures.[22−24] Angle-resolved XPS, where the angle between the sample and analyzer is changed to determine a depth profile, is often challenging for AP-XPS due to geometric constraints.

Results

Conclusion