Ambient pressure phase transitions over Ir(1 1 1): at the onset of CO oxidation. (12th October 2017)

• Record Type: Journal Article
• Authors: Johansson, N; Andersen, M; Monya, Y; Andersen, J N; Kondoh, H; Schnadt, J; Knudsen, J
• Is Part Of: Journal of physics. Volume 29:Number 44(2017)
• Publication Date: 2017-10-12
• Subjects: CO oxidation -- Ir(1 1 1) -- Pt(1 1 1) -- XPS -- DFT -- APXPS; Condensed matter -- Periodicals; Matière condensée -- Périodiques; Vaste stoffen; Vloeistoffen; Natuurkunde; Electronic journals; Computer network resources; 530.4105
• DOI: 10.1088/1361-648X/aa8a44
• Languages: English
• ISSNs: 0953-8984

Abstract

Abstract: In this study we report on the adsorbate structures on an Ir(1 1 1) surface during the phase transition from the inactive to the active state during CO oxidation. The CO oxidation over Pt(1 1 1) is used as a reference case. Where Pt(1 1 1) either is inactive and CO covered or active and O covered, Ir(1 1 1) exhibits a transition state with co-existing chemisorbed O and CO. The observed structural differences are explained in terms of DFT-calculated adsorption energies. For Pt(1 1 1) the repulsive CO–O interaction makes co-existing chemisorbed CO and O unfavourable, while for Ir(1 1 1) the stronger O and CO adsorption allows for overcoming the repulsive interaction. At the onset of CO oxidation over Ir(1 1 1), a CO structure containing defects forms, which enables O2 to dissociatively adsorb on the Ir(1 1 1) surface, thus enabling the CO oxidation reaction. At the mass transfer limit, the Ir(1 1 1) surface is covered by a chemisorbed O structure with defects; hence, the active surface is predominately chemisorbed O covered at a total pressure of 0.5 mbar and no oxide formation is observed.