In-Situ Oxygen Isotopic Exchange Vibrational Spectroscopy of Rhenium Oxide Surface Structures on Cerium Oxide
Blake MacQueen, Benjamin Ruiz-Yi, Michael M. Royko, Andreas Heyden, Yomaira J. Pagán‐Torres, Christopher T. Williams, Jochen Lauterbach
Abstract
The surface structures of ReOx supported on CeO2 at low loadings have been elucidated through 18O isotopic exchange Raman spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The ReOx 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 cross-linked ReOx species. The isotopic exchange Raman spectroscopy shows a red shift resulting from the 18O 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 18O 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 ReOx–Pd/CeO2 catalyst and deoxydehydration over the ReOx/CeO2 catalyst.