Ambient pressure phase transitions over Ir(111): at the onset of CO oxidation

作者：Johansson N; Andersen M; Monya Y; Andersen J N; Kondoh H; Schnadt J; Knudsen J^*

来源：Journal of Physics: Condensed Matter , 2017, 29(44): 444002.

DOI：10.1088/1361-648X/aa8a44

• CO oxidation
• Ir(111)
• Pt(111)
• XPS
• DFT
• APXPS

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 O-2 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.

• 出版日期2017-11-8