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

Abstract

A novel operando spectroscopic approach combining multiwavelength and time-resolved Raman spectroscopy with gasphase 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.

Application of Raman Spectroscopy to Working Gas Sensors: From in situ to operando Studies

“…So far Raman spectroscopic studies on gas sensors have been restricted to visible or NIR excitation. However, the use of UV excitation may offer several advantages as has been demonstrated in the context of catalytic materials [48,49]: First, fluorescence effects can be prevented. As for UV excitation, the Raman signal is widely separated in energy from the fluorescence emission.…”

Activity, Selectivity and Initial Degradation of Iron Molybdate in the Oxidative Dehydrogenation of Ethanol

“…Due to this attractiveness, different catalyst systems have been studied for ethanol ODH. The main classes of investigated catalysts are supported metal oxides, mainly supported VO x , [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] mixed metal oxides, [25,26] supported metal catalysts [27][28][29][30] or carbon-based catalysts. [31][32][33] Supported vanadium oxide catalysts show high activity in the ODH of ethanol.…”

High Surface Area VOx/TiO2/SBA-15 Model Catalysts for Ammonia SCR Prepared by Atomic Layer Deposition

“…According Figure 1b shows the corresponding Raman spectra at 532 nm excitation. The spectrum of TiO 2 /SBA-15 is characterized by broad features typical for amorphous silica dominating the weaker (surface) titania contributions [62]. Major features include the band at around 450-550 cm −1 associated with four-membered rings (D 1 ), and the broad band at around 600-900 cm −1 assigned to symmetrical Si-O-Si stretching and three-membered rings (D 2 ) [63].…”