ReO
x/CeO
2 and ReO
x-Pd/CeO
2 are important catalysts for the deoxydehydration (DODH) and simultaneous hydrodeoxygenation (S-HDO) of biomass derived sugars. However, the surface structures of the ReO
x in these catalysts have only been theorized using Density Functional Theory (DFT) calculations in the literature
1,2. In our work
3, the surface structures of ReO
x supported on CeO
2 at low loadings have been elucidated through
18O isotopic exchange Raman spectroscopy and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). We found that 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 which contains a hydroxyl group, and a crosslinked ReO
x 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 using the model for a simple rigid diatomic molecule. Time resolved DRIFTS showed significant exchange of
18O over time and further reconfirmed the results from the Raman spectroscopy. Our results show that there are multiple isolated monomeric structures and an oligomeric structure of ReO
x present when supported CeO
2.
References
(1) Ota, N.; Tamura, M.; Nakagawa, Y.; Okumura, K.; Tomishige, K. Performance, Structure, and Mechanism of ReOx âPd/CeO2 Catalyst for Simultaneous Removal of Vicinal OH Groups with H2. ACS Catal. 2016, 6 (5), 3213â3226.
(2) Xi, Y.; Yang, W.; Ammal, S. C.; Lauterbach, J.; Pagan-Torres, Y.; Heyden, A. Mechanistic Study of the Ceria Supported, Re-Catalyzed Deoxydehydration of Vicinal OH Groups. Catal. Sci. Technol. 2018, 8 (22), 5740â5752.
(3) MacQueen, B.; Ruiz-Yi, B.; Royko, M.; Heyden, A.; Pagan-Torres, Y. J.; Williams, C.; Lauterbach, J. In-Situ Oxygen Isotopic Exchange Vibrational Spectroscopy of Rhenium Oxide Surface Structures on Cerium Oxide. J. Phys. Chem. C 2020, 124 (13), 7174â7181.
