In situ X-ray photoelectron spectroscopy of model catalysts: At the edge of the gap

TL;DR

This study combines high-pressure X-ray photoelectron spectroscopy and kinetic Monte Carlo simulations to investigate active phases in CO oxidation on Pd(100), revealing stable oxide and O-covered surfaces as key active states.

Contribution

It introduces a combined experimental and computational approach to identify active catalyst phases under near-ambient conditions, highlighting the role of surface oxides and O-covered surfaces.

Findings

Both O-covered Pd(100) and surface oxide are stable and active phases.

No adsorbed CO detected during high CO2 production, due to short residence time and mass transfer limits.

Surface oxides contribute significantly to catalytic activity.

Abstract

We present a High-Pressure X-ray Photoelectron Spectroscopy (HP-XPS) and first-principles kinetic Monte Carlo study addressing the nature of the active surface in CO oxidation over Pd(100). Simultaneously measuring the chemical composition at the surface and in the near-surface gas-phase, we reveal both O-covered pristine Pd(100) and a surface oxide as stable, highly active phases in the near-ambient regime accessible to HP-XPS. Surprisingly, no adsorbed CO can be detected during high CO2 production rates, which can be explained by a combination of a remarkably short residence time of the CO molecule on the surface and mass-transfer limitations in the present set-up.