(705b) In-Situ Oxygen Isotopic Exchange Vibrational Spectroscopy of Rhenium Oxide Surface Structures on Cerium Oxide
AIChE Annual Meeting
2020
2020 Virtual AIChE Annual Meeting
Catalysis and Reaction Engineering Division
Catalyst Synthesis and Design I: Oxides
Tuesday, November 17, 2020 - 8:15am to 8:30am
ReOx/CeO2 and ReOx-Pd/CeO2 are important catalysts for the deoxydehydration (DODH) and simultaneous hydrodeoxygenation (S-HDO) of biomass derived sugars. However, the surface structures of the ReOx in these catalysts have only been theorized using Density Functional Theory (DFT) calculations in the literature1,2. In our work3, 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). We found that 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 which contains a hydroxyl group, and a crosslinked 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 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 ReOx present when supported CeO2.
References
(1) Ota, N.; Tamura, M.; Nakagawa, Y.; Okumura, K.; Tomishige, K. Performance, Structure, and Mechanism of ReOx –Pd/CeO2 Catalyst for Simultaneous Removal of Vicinal OH Groups with H2. ACS Catal. 2016, 6 (5), 3213–3226.
(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), 5740–5752.
(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), 7174–7181.