XPS study of oxidation of rhenium metal on ?-Al2O3 support

In SituStudies of Carbon Monoxide Oxidation on Platinum and Platinum–Rhenium Alloy Surfaces

“…However, the binding energy is closer to 44.8 eV, which is the lowest of the Re +6 values reported in the literature. 38,58-61 At 500 K, the Re signal is 11% of that at 300 K, and this loss of Re is attributed to sublimation of Re 2 O 7 . For the Re film exposed to CO oxidation conditions without prior 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 19 oxidation, substantial oxidation is observed even at 400 K (Figure 7b), indicating the reaction mixture of CO and O 2 is still highly oxidizing despite the pre...…”

“…This peak is attributed to Re +5 , given that the binding energies for Re +6 (44.8-45.4 eV) are too high, and the binding energies of Re +4 (42.3-42.8 eV) are too low. 38,[58][59][60][61] At 450 K, Re +5 is the primary oxidation state, but there is a smaller feature at 45.2 eV assigned to Re +6 , and this binding energy species is also observed as a shoulder in the spectrum at 295 K.…”

“…37 NAP-XPS experiments are used here to investigate oxidation states of Re and surface species during reaction at pressures of 550 mTorr, and this represents the first study of Re oxidation states for Pt-Re surfaces under reaction conditions. Furthermore, these experiments allow the stability of ReO x in an oxidizing reaction environment to be probed, and this is important because Re 2 O 7 is known to sublime at relatively low temperatures ranging from 423 K for supported particles 38 to 500 K for bulk rhenium oxide. 39 The results from these investigations demonstrate that CO binds less strongly to the Pt-Re alloy surface than to Pt(111), given that very little CO adsorbs during CO oxidation at 450 K on Pt-Re compared to Pt(111).…”

“…The incident photon energy was 545 eV. The vertical scale for the bottom panel is twice that for the top panel.sublimation, given that Re 2 O 7 is known to be highly volatile and reported to desorb at temperatures as low as 423 K-600 K 38,39,…”

Electrocatalysis of the hydrogen evolution reaction by rhenium oxides electrodeposited by pulsed-current

“…As a result, the binding energy may vary as a function of the closest neighbors, which modify the electronic environment surrounding each site [21,24]. Additionally, the differences in Re oxidation states on the surface and the FWHM of the peaks could be an indication that the electrodeposited material is a mixture of oxides of various valences that are not fully integrated with each other.…”