Observing phase changes in real time on ultrathin Iron oxide surfaces

University essay from Lunds universitet/Synkrotronljusfysik; Lunds universitet/Fysiska institutionen

Abstract: Studying catalysts under such non-equilibrium conditions is a step towards approaching more realistic reaction conditions for working catalysts. Reactivity during phase changes of ultra-thin FeO2 films grown on Pt(111) are studied in situ with Ambient Pressure X-ray Photo Emission Spectroscopy and Quadrupole Mass Spectrometry, while running the CO oxidation reaction at 160°C and 0:6 mbar. These phase changes are induced by rapidly changing the gas composition of the CO:O2 feed gas. The composition is changed so that series of 16-second pulses of CO are sent to the sample. My study showed that CO in the first few pulses is completely oxidised while only the first part of later pules is oxidised. This partial oxidation is explained by gradual CO poisoning of bare Pt(111) patches formed between FeO2 islands due to dewetting of the FeO2 film. During CO poisoning, core level shifts indicate a change from FeO2 trilayer to an oxide film with more FeO bilayer character. The activity of the FeO2/Pt(111) sample increased gradually and reached higher values than the Pt(111) reference after an incubation time of about one hour.

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