In situ oxidation of CO on a curved Pt(111) surface in near- ambient pressure conditions

Abstract

The study of heterogeneous catalysis using metal single crystal has been a wide research field since long. Nevertheless, neither the real mechanism nor the role of atomic terraces/steps has been clearly identified, which makes the development of efficient (nanostructured) catalysts harder. Crystal surfaces undergo structural/chemical changes during catalytic reactions, so in situ studies are required for a real understanding of the process. For this reason we have carried out near-ambient pressure X-ray photoemission (NAP-XPS) experiments of the CO oxidation by O2 on a curved Pt crystal around the (111) face. By scanning the small X-ray beam, XPS spectra were collected all over the surface, observing a variation of the active species across the different crystallographic planes. The figure below shows the C 1s XPS spectra taken when increasing the temperature during the ignition process at the (111) face (left side) and at a fixed temperature (T=525K) scanning over the curved crystal (rigth side). The temperature scan at the (111) plane (left side panel) shows that, below the onset of the catalytic reaction, the surface is covered with two carbon species, namely chemisorbed CO (Chem-CO) and graphitic carbon ("C"). When the ignition starts, the "C" species is eliminated first, and then the Chem-CO is displaced by chemisorbed oxygen. This process is accompanied by a rightward shift of the gas phase components. The rigth panel demonstrates that the relative intensity of each "C" and Chem-CO varies across the curved surface, indicating a progressively increasing activity from the low active edge on top (A stepped surfaces), to the (111) center, and to the highly active B-stepped edge.