Photoelectron spectroscopy (XPS) and thermogravimetry (TG) of pure and supported rhenium oxides 1. Pure rhenium compounds

Abstract

To investigate the interaction of rhenium with several supports, a preliminary study on pure rhenium compounds has been carried out in order to achieve a better understanding of their surface chemical properties. To this end X‐ray photoelectron spectroscopy (XPS) and thermogravimetry (TG) methods have been applied. The results show that metallic rhenium, ReO2 and ReO3 are covered with Re(VII). By heating in H2, NH4ReO4 and rhenium oxides are reduced to metallic rhenium in different temperature ranges. In the case of Re2O7 a spillover effect has been found when platinum is present. For ReO3 and ReO2 a morphological model has been described on the basis of combined XPS, TG and surface area measurements. The binding energy values of the different rhenium oxidation states have been assessed and their variation with the oxidation number briefly discussed.

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

“…Other data demonstrated that ReO 3 is the product of oxidation of Re in Re/γ -Al 2 O 3 catalyst above 400 • C [16]. It was also reported that at or above 300 • C rhenium heptaoxide is the main product of oxidation of Re supported on alumina [15,21] as well as rhenium powder [27] and thin Re films [28]. As can be seen, the interaction of oxygen with Re/γ -Al 2 O 3 catalyst is a complex process and depends mainly on the temperature and the rhenium loading [13,14,16,18,19].…”

The Oxidation of Rhenium and Identification of Rhenium Oxides During Catalytic Partial Oxidation of Ethylene: An In-Situ XPS Study

“…[22][23][24] The existence of a Re 5+ species in binary oxides is inconclusive; however, in rhenium-oxide bronzes (e.g. rhenium oxides alloyed other cationic elements), rhenium oxidation states of +4, 5,6 and 7 are all possible.…”

“…Since the 1970s, many XPS studies have been performed to examine the chemical state of rhenium catalyst surfaces; however, due to instrumentation limitations, these studies were performed ex-situ. [14,20,23,[31][32][33][34][35] The problem with ex-situ studies is that the rhenium oxidation states that are measured postreaction can differ substantially from the species that are present in-situ.…”

Metallic Re–Re bond formation in different MRe2O6 (MFe, Co, Ni) rutile-like polymorphs: The role of temperature in high-pressure synthesis

“…The shifts in binding energies between Re4f 7/2 and Re4f 5/2 peaks of Re +4 in ReO 2 and Re +6 in ReO 3 are significant [24]. The authors of [25] have established an exponential dependence of the binding energy on the oxidation state of Re in the compounds NH 4 ReO 4 , Re 2 O 7 , ReO 3 , ReO 2 and metallic Re without consideration of the underlying structures. However, the difference in the positions of the Re4f 7/2 peaks for Re +7 in NH 4 ReO 4 and Re 2 O 7 points out an influence of the structural features on the XPS spectra: in ammonium perrhenate only corner-sharing ReO 4 -tetrahedra exist, in contrast to both corner-sharing ReO 4 -tetrahedra and ReO 6 -octahedra in Re 2 O 7 .…”