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.