Impact of the Si/Al ratio on the ethanol/water coadsorption on MFI zeolites revealed using original quantitative IR approaches.

Advanced IR vibrational spectroscopic techniques, e.g., using a coupled gravimetric-IR surface analyzer (AGIR) and a high-throughput in situ IR cell (Carroucell), have been used for the quantitative studies of the adsorption and coadsorption of ethanol and water on MFI zeolites with different Si/Al ratios. The AGIR coupling is a powerful tool for the accurate determination of the molar adsorption coefficients during coadsorption experiments since their evaluation is based on the measurement of the exact amount of adsorbed species. The use of the Carroucell set up allows characterizing all the samples simultaneously, strictly in the same gaseous and temperature environment. The molar absorption coefficients of pure adsorbed ethanol and water are determined: their values are constant whatever the Si/Al ratio of the MFI zeolites. Moreover, these coefficients are found to be identical in the case of the water-ethanol coadsorption experiments. Their use allows obtaining the exact quantity of each adsorbate specie in the binary system. At low partial pressures, the unary water adsorption experiments suggest that the amount of adsorbed water results mainly from the preferential adsorption on Brønsted acid sites in tetrameric clusters. In contrast, the adsorption of EtOH occurs on both silanol groups and Brønsted acid sites (BASs). The effect of the Si/Al ratio is only observed at relatively low partial pressures. The effect of the Si/Al ratio on the ethanol adsorption capacity is also investigated. This study directs the choice of an appropriate zeolite once it is used in membranes for drying ethanol.

In Situ FTIR Reactor for Monitoring Gas-Phase Products during a (Photo)catalytic Reaction in the Liquid Phase.

Various catalytic and photocatalytic reactions in the liquid phase give rise to gas products. Therefore, the identification and quantification of these products are of high importance and are even essential for some reactions. In this paper, a new in situ FTIR reactor is designed and used for analyzing the gas headspace of a (photo)catalytic reaction in solution. It allows the identification and quantification of the gas-phase products of a liquid reaction under operating conditions and in real time. The new reactor has been tested in three representative photocatalytic reactions widely studied as model reactions in the liquid phase: i.e., (i) decomposition of formic acid, (ii) oxidation of methylene blue, and (iii) reduction of CO2. The validity of the results has been confirmed by analyzing the headspace at the end of the reaction using gas chromatography technique. The new reactor opens the possibility to follow online the (photo)catalyst activity. This is useful for ensuring the stability of the catalyst and studying the evolution of the selectivity during the reaction. The nondestructive behavior of the FTIR technique allows its coupling with other techniques for obtaining complementary results. The new reactor setup is easy to handle and to ship and is very efficient, which makes it very suitable for performing complementary, fast and/or preliminary studies.