Potential of UV–Raman Spectroscopy for Characterization of Sub-monolayer MoO_xModel Catalysts at Ambient Pressure

Abstract

UV-Raman spectroscopy is demonstrated to be a valuable tool to study molybdenumoxide model catalysts at ambient pressure while visible light Raman yields no information. UV-Raman offers the possibility to characterize MoO x /Al 2 O 3 /Si and MoO x /SiO 2 / Si model systems with sub-monolayer loading of MoO x even though the surface area of a Si-wafer is much lower than that of a bulk support. Anchoring of MoO x onto Al 2 O 3 /Si and SiO 2 /Si results in similar molybdenum oxide compounds as for bulk catalysts.

Oligomerization of Supported Vanadia: Structural Insight Using Surface-Science Models with Chemical Complexity

“…The two sharp features at 1557 and 2334 cm –1 originate from gas-phase molecular oxygen and nitrogen, respectively. , For the weakly loaded samples, the oxygen feature also exhibits some rotational fine structure . Besides, substrate features due to crystalline silicon are detected at 512 and ∼940 cm –1 . ,, In particular, the peak at 512 cm –1 , which is slightly red-shifted due to the sample temperature, corresponds to a Si–Si stretching mode, while the broad band at ∼940 cm –1 is assigned to the Si overtone region…”

“…Such an approach is beneficial when studying specific structural aspects, as in this work. While we are not aware of any Raman studies on such planar vanadia systems, Mojet et al investigated similar model systems for dispersed molybdena using UV Raman spectroscopy …”

“…While we are not aware of any Raman studies on such planar vanadia systems, Mojet et al investigated similar model systems for dispersed molybdena using UV Raman spectroscopy. 16 There are only a few techniques that provide sufficient sensitivity to obtain information on vibrational modes of surface species on planar model systems but at the same time allow in situ experiments at elevated temperatures in air. Regarding Raman spectroscopic techniques, these include resonance Raman (RR) spectroscopy, surface-enhanced Raman spectroscopy (SERS), and tip-enhanced Raman spectroscopy (TERS).…”

CoMo/γ-Al2O3 Catalysts Prepared by Reverse Microemulsion: Synthesis and Characterization

“…Furthermore, it was found that the bands corresponding to the Mo-O-Mo links increased proportionally when increasing the bands corresponding to the MoO 2t links [2,41,43]. This suggests that there was an increase in the number of bridges of Mo, which implied high dispersion of Mo on the support [40,44]. Additionally, bands between 905 and 918 cm −1 for the C5 and CoMoind catalysts were attributed to the presence of molybdate CoMoO 4 species, either isolated or polymerized, involving a strong interaction with the support.…”

“…For C1 and C2 catalysts, a band in the range between 970 and 1100 cm −1 was detected and highly dispersed MoO 4 tetrahedral species can be assigned in agreement with MAS-NMR results. It is likely that these metal loadings did not reach the MoOx monolayer formation [44,47]. Moreover, the bands appearing between 200 and 400 cm −1 were attributed to Mo monomeric species [33].…”