The surface structures of ReO x supported on CeO 2 at low loadings have been elucidated through 18 O isotopic exchange Raman spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The ReO x is present in four distinct structures, a di-oxo structure with two ReO terminal bonds, a mono-oxo species that contains one ReO terminal bond, a mono-oxo species that contains a hydroxyl group, and a crosslinked ReO x species. The isotopic exchange Raman spectroscopy shows a red shift resulting from the 18 O exchange in the OReO, ReO, Re−OH, and Re−O−Re species, which allowed for the deconvolution of the various structures. Time-resolved DRIFTS showed significant exchange of 18 O over time and reconfirmed the results from the Raman spectroscopy. The presence of multiple surface species supports the existence of competing reaction mechanisms for the simultaneous hydrodeoxygenation over the ReO x −Pd/ CeO 2 catalyst and deoxydehydration over the ReO x /CeO 2 catalyst.

Multiprincipal element high entropy alloys stabilized as a single alloy phase represent a new material system with promising properties, such as high corrosion and creep resistance, sluggish diffusion, and high temperature tensile strength. However, the mechanism of stabilization to form single phase alloys is controversial. Early studies hypothesized that a large entropy of mixing was responsible for stabilizing the single phase; more recent work has proposed that the single-phase solid solution is the result of mutual solubility of the principal elements. Here, we demonstrate the first self-consistent study of the relative importance of these two proposed mechanisms. In situ high-throughput synchrotron diffraction studies were used to monitor the stability of the single phase alloy in thin-film (Al1-x-yCuxMoy)FeNiTiVZr composition spread samples. Our results indicate that a metastable solid solution can be captured via the rapid quenching typical of physical vapor deposition processes, but upon annealing the solid-solution phase stability is primarily governed by mutual miscibility.

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<p>PDF file, 113KB, A derivation of the mathematical model of biodistribution is presented.</p>

<p>PDF file, 54KB, Model parameters and citations for estimates.</p>