Adsorbate-induced structural evolution changes the mechanism of CO oxidation on a Rh/Fe₃O₄(001) model catalyst

Abstract

The structure of a catalyst often changes in reactive environments, and following the structural evolutionis crucial for the identification of the catalyst's active phase and reaction mechanism. Here we present anatomic-scale study of CO oxidation on a model Rh/Fe3O4(001)"single-atom"catalyst, which has a verydifferent evolution depending on which of the two reactants, O2or CO, is adsorbedfirst. Using tempera-ture-programmed desorption (TPD) combined with scanning tunneling microscopy (STM) and X-rayphotoelectron spectroscopy (XPS), we show that O2destabilizes Rh atoms, leading to the formation ofRhxOyclusters; these catalyze CO oxidationviaa Langmuir-Hinshelwood mechanism at temperatures aslow as 200 K. If CO adsorbsfirst, the system is poisoned for direct interaction with O2, and CO oxidationis dominated by a Mars-van-Krevelen pathway at 480 K.