Operando XANES-FTIRS study of dehydrogenation of ethanol to acetaldehyde over V₂O₅/TiO₂ and V₂O₅/CeO₂ catalysts

An operando study of non-oxidative and oxidative dehydrogenation of ethanol to acetaldehyde over V₂O₅/TiO₂ and V₂O₅/CeO₂ catalysts was performed using X-ray absorption near-edge structure (XANES) and Fourier-transform infrared spectroscopy (FTIRS). The experiments were carried out at atmospheric pressure within a temperature range of 50-300 °C. XANES was employed to probe the coordination and oxidation states of vanadium, cerium, and titanium in the catalysts under working conditions. To quantitatively analyze the XANES data, a machine learning-based approach was implemented. FTIRS was used to evaluate catalytic performance by analyzing gas-phase reactants and products. Both catalysts exhibit activity in the dehydrogenation of ethanol to acetaldehyde. In the absence of gas-phase O₂, no acetic acid, CO, or CO₂ was detected. However, these by-products were formed upon the introduction of O₂ into the reaction feed over the V₂O₅/TiO₂ catalyst. The V₂O₅/CeO₂ catalyst demonstrates higher activity than V₂O₅/TiO₂ in the oxidation of ethanol at low temperatures, with turnover frequencies (TOFs) of 1.3 and 0.5 h^-1 at 100 °C, respectively. According to the XANES measurements, the support material strongly affects the redox properties of vanadia. It was found that ethanol reduces V⁵⁺ cations to V⁴⁺ and V³⁺ in the V₂O₅/TiO₂ catalyst but does not affect the chemical state of titanium. Conversely, in the V₂O₅/CeO₂ catalyst, V⁵⁺ cations are reduced to V⁴⁺ only, which is accompanied by a partial reduction of Ce⁴⁺ cations by ethanol. The average coordination numbers of vanadium cations were obtained under these conditions for both catalysts. The effect of the support material on the catalytic properties of the supported vanadium oxide is discussed.