Regensburg 2016 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 64: Oxides and Interfaces: Adsorption II
O 64.6: Vortrag
Mittwoch, 9. März 2016, 16:15–16:30, H6
N2O to N2 conversion on reduced ceria surface: NEXAFS and IRRAS studies — •Alexei Nefedov, Chengwu Yang, and Christof Wöll — Karlsruhe Institute of Technology, Karlsruhe, Germany
Ceria, one of the most reducible metal oxides, has proven to be a highly active catalyst for NOx reduction to N2. To monitor this conversion the NEXAFS and IRRA spectroscopies have been applied in a time-resolved fashion. The stoichiometric CeO2 single crystals and powders were annealed at elevated temperatures in vacuum to create surface oxygen vacancies. N2O exposure was achieved by backfilling up to 10−9 mbar at sample temperatures typically below 120 K. The NEXAFS measurements were carried out at the synchrotron facility BESSY II and for IRRAS experiments we used a novel UHV-IR spectrometer. In the NEXAFS spectra, two intense resonances (401.2 eV and 404.8 eV) with equal intensities are observed. These resonances decrease in parallel over time and this decrease is explained by conversion of N2O to N2 over reduced CeO2. IRRAS data confirm NEXAFS results. After N2O adsorption only one band at 2250 cm−1 is observed, which can be described as a nitrogen-nitrogen asymmetric stretching vibration. After the temperature increase as well as after the UV irradiation the band intensity goes down. Comparison of grazing emission XP spectra before and after N2O treatment indicates N2O donated oxygen atom to the oxygen vacancy and re-oxidized the reduced CeO2.