CO oxidation on Pd(100) at technologically relevant pressure conditions: A first-principles kinetic Monte Carlo study

TL;DR

This study uses first-principles kinetic Monte Carlo simulations to investigate the stability of surface oxides on Pd(100) during CO oxidation at realistic pressure conditions, revealing dynamic formation and decomposition of oxides.

Contribution

It provides the first detailed kinetic Monte Carlo analysis of surface oxide stability on Pd(100) under technologically relevant conditions, highlighting the role of local pressure and temperature fluctuations.

Findings

Surface oxide is stabilized at ambient conditions near the most relevant CO:O2 ratios.

Temperature fluctuations influence the formation and decomposition of surface oxides.

Steady-state operation involves dynamic oxide formation and reduction processes.

Abstract

The possible importance of oxide formation for the catalytic activity of transition metals in heterogenous oxidation catalysis has evoked a lively discussion over the recent years. On the more noble transition metals (like Pd, Pt or Ag) the low stability of the common bulk oxides suggests primarily sub-nanometer thin oxide films, so-called surface oxides, as potential candidates that may be stabilized under gas phase conditions representative of technological oxidation catalysis. We address this issue for the Pd(100) model catalyst surface with first-principles kinetic Monte Carlo (kMC) simulations that assess the stability of the well-characterized (sqrt{5} x sqrt{5})R27 surface oxide during steady-state CO oxidation. Our results show that at ambient pressure conditions the surface oxide is stabilized at the surface up to CO:O2 partial pressure ratios just around the catalytically most relevant stoichiometric feeds (p(CO):p(O2) = 2:1). The precise value depends sensitively on temperature, so that both local pressure and temperature fluctuations may induce a continuous formation and decomposition of oxidic phases during steady-state operation under ambient stoichiometric conditions.