Operando Multiwavelength and Time-Resolved Raman Spectroscopy: Structural Dynamics of a Supported Vanadia Catalyst at Work

A novel operando spectroscopic approach combining multiwavelength and time-resolved Raman spectroscopy with gas-phase Fourier transform infrared (FTIR) spectroscopy is presented, supported by in situ UV–vis diffuse reflectance (DR) spectroscopy. The potential of this approach is demonstrated in a case study of the oxidative dehydrogenation (ODH) of ethanol over a silica-supported vanadia catalyst. The structural dynamics of the catalyst upon switching from oxidative to reactive conditions was extensively studied by Raman spectroscopy with different excitation wavelengths in the visible and UV, exploiting resonance effects in a targeted manner. Time-dependent correlation of Raman and IR spectra over several reaction cycles allows identification of active vanadia surface structures. Detailed Raman spectroscopic analysis reveals that the adsorption of ethoxy species onto dispersed VO x structures occurs via opening of both V–O–Si and V–O–V bonds. During reaction, large oligomeric VO x structures are decomposed into smaller units. Combined Raman and UV–vis results show that these structural changes cannot be completely regenerated.