Monolayer iron oxide film on platinum promotes low temperature CO oxidation

Abstract

CO oxidation on a clean Pt(1 1 1) single crystal and thin iron oxide films grown on Pt(1 1 1) was studied at different CO:O 2 ratios (between 1:5 and 5:1) and partial pressures up to 60 mbar at 400–450 K. Structural characterization of the model catalysts was performed by scanning tunnelling microscopy, low energy electron diffraction, Auger electron spectroscopy and temperature-programmed desorption. It was found that monolayer FeO(1 1 1) films grown on Pt(1 1 1) were much more active than clean Pt(1 1 1) and nm-thick Fe 3O 4(1 1 1) films at all reaction conditions studied. Post-characterization of the catalysts revealed that at CO:O 2 > 1 the FeO(1 1 1) film dewets the Pt surface with time, ultimately resulting in highly dispersed iron oxide particles on Pt(1 1 1). The film dewetting was monitored in situ by polarization-modulated infrared reflection absorption spectroscopy. The reaction rate at 450 K exhibited first order for O 2 and non-monotonously depended on CO pressure. In O 2-rich ambient the films were enriched with oxygen while maintaining the long-range ordering. Based on the structure-reactivity relationships observed for the FeO/Pt films, we propose that the reaction proceeds through the formation of a well-ordered, oxygen-rich FeO x (1 < x < 2) film that reacts with CO through the redox mechanism. The reaction-induced dewetting in fact deactivates the catalyst. The results may aid in our deeper understanding of reactivity of metal particles encapsulated by thin oxide films as a result of strong metal–support interaction.