Operando Reactor-Cell with Simultaneous Transmission FTIR and Raman Characterization (IRRaman) for the Study of Gas-Phase Reactions with Solid Catalysts.

Raman and transmission FTIR spectroscopic techniques have been coupled in a new homemade reactor-cell designed in a joint CSIC-LCS collaboration. The setup is easily adapted to any FTIR and fiber-coupled Raman spectrometers and gas analysis techniques. It allows for simultaneous operando FTIR and Raman spectroscopic measurement, which provide complementary characterization of adsorbed species, reaction intermediates, and structural properties of the catalyst. This system was validated with the study of vanadium-based catalysts during propane oxydehydrogenation (ODH). The combined use of both spectroscopies with gas analysis techniques to measure the activity contributes to the understanding of propane ODH and the identification of the role of different oxygen species bound to vanadium sites. For example, the simultaneous characterization of the catalyst under the same conditions by IR and Raman confirms that the V═O mode has the same frequency in both spectroscopies and that bridging oxygen sites (V-O-V, V-O-Zr) present higher activity than terminal V═O bonds. These results demonstrate the high potential of the new simultaneous transmission IR-Raman operando rig to correlate the activity and the structure of catalysts, thus assisting the rational design of catalytic processes.

Synthesis of Vanadium Oxide Nanofibers with Variable Crystallinity and V5+/V4+ Ratios.

Tailoring the morphological, chemical, and physical properties of vanadium oxides (VOx) is crucial to optimize their performance in current and future applications. The present contribution proposes a new route to obtain VOx nanofibers with different V4+/V5+ ratios and crystallinity. The method involves the exclusive electrospinning of water-free NH4VO3-saturated solutions including a reductant. Subsequent air-annealing under suitable conditions yields vanadium oxide fibers of 20-90 nm diameter and 10-50 m2/g surface area. The presence of the reductant gives rise to VOx nanofibers with a considerable proportion of V4+. Then, the right choice of the calcination heating rate and temperature permits to modify the V4+/V5+ ratio as well as the crystalline phase and crystallite size of the fibers. With the proposed methodology, long-range continuous single-phase orthorhombic V2O5 and monoclinic V3O7 nanofibers are obtained.