Detailed Analysis of the Raman Vibrational Structure of Vanadia in VOx/CeO2: A Combined Experimental and Theoretical Approach

Supported vanadia is an important catalyst for oxidation reactions but its properties and catalytic activity heavily depend on the support material. Ceria is a promising support due to its reducibility and active participation in many oxidation reactions. To understand these catalysts at work, operando spectroscopy is required, which can be difficult to interpret. To obtain a fundamental, nuclearity-dependent understanding of the vibrational structure of VOx/CeO2, we combined Raman characterization with density functional theory (DFT) by calculating vibrational frequencies and Raman intensities based on established vanadia structures on support structures with (4 × 4) periodicity. Monomeric and oligomeric structures were simulated based on VO and VO2 clusters, resulting in VnOn (n = 1–3) and VnO2n (n = 1–7) oligomers. The latter were combined based on weighting factors determined from the experimental vanadyl fine structure and the thermodynamic stability of the clusters, yielding a simulated spectrum of the nuclearity distribution. Using this approach, vanadium coverage effects could be simulated, resulting in an overall agreement between experimental and theoretical spectra and providing nuclearity-dependent insight into the vibrational spectrum of VOx/CeO2, including the interface region and the vanadyl fine structure. Our study highlights the importance of DFT calculations to facilitate the assignment of spectroscopic features and obtain a detailed understanding of catalytic materials.