Fig. 3
From: Visualizing atomic-scale redox dynamics in vanadium oxide-based catalysts
In situ measurements of the vanadium oxidation state by EELS. a Vanadium L2,3-edge region of EEL spectra recorded from both 2 and 0.5 monolayer VOx/TiO2 particles, normalized to the Ti L2,3 edge intensity. For the 0.5 monolayer sample, the signal has been multiplied by four in order to show the spectra from the two samples on the same intensity scale. For both samples, the V L-edge shows a marked shift in energy loss as the conditions were changed in situ from neutral (room temperature, vacuum), to reducing (300 °C, vacuum), and to oxidizing (300 °C, 1 mbar O2) conditions. A spectrum extracted from a STEM SI is included for comparison. The energy losses of the V L3 peak for two bulk vanadium oxides33 are also indicated. b Position and normalized height of the V L3 peak, measured by fitting a Gaussian function to background subtracted EEL spectra, obtained during heating of the 2 monolayer sample in 1 mbar O2. At 300 °C, a plateau was reached with a stable vanadium oxidation state. Above ca. 450 °C, approximately half of the 2 monolayers of vanadium oxide was lost, accompanied by a small further oxidation. The difference of < 0.2 eV of the V L3-peak position between multiple measurements illustrates the high precision of the EELS measurement
