Rhenium

Typically considered to be one of the most stable elements due to its high melting and boiling points, rhenium is often found in nickel based superalloys, but also finds use in olefin metahtesis and reforming catalysis. Rhenium can exhibit multiple oxidation states, with +7, +6, +4 and +2 the most common in materials analysed by XPS.

Figure 1, shows the spectra of a partially oxidised rheinium foil exhibiting metallic Re (green), ReO2 (blue) and Re2O7 (yellow) states.

Figure 1. Rhenium foil with Re, ReO2 and Re2O7 species present. Note for fitting the Shirley background has been offset suggesting a different background may be more suitable here.

High valence rhenium oxides can undergo disproportionation during XPS analysis [1], so a suitable methodology, such as rapid acquisition and recording the Re(4f) region first and again at the end should be considered.

Material Re(4f 7/2) Binding Energy / eV Reference
Re Metal 40.4 (Calibrated to Fermi Level) [2]
Re2O7 46.8 (Calibrated to C(1s) at 284.8 eV) [1, 2]
NH4ReO4 46.3 (Calibrated to C(1s) at 284.8 eV) [2]
ReO2 43.0 (Std. Dev. of 0.6 eV) [2] , ([3])
ReO3 44.2 (Std. Dev of 1.3 ev) [2] , ([3])
Table 1. Binding energies of common Re states

References

[1] S. Iqbal, M. L. Shozi and D. J. Morgan, X‐ray induced reduction of rhenium salts and supported oxide catalysts, Surf. Inter. Anal. 49 (2017) 223-226. Read it online here

[2] Measured at HarwellXPS on a Thermo K-Alpha+ spectrometer, which has been calibrated using the internal ISO calibration method.

[3] Average of measurements from NIST. NIST Standard Reference Database 20, Version 4.1, Visit the site

Created: February 15, 2021