Topology-dependent hydrocarbon transformations in the methanol-to-hydrocarbons reaction studied by operando UV-Raman spectroscopy

Abstract

Probing hydrocarbon transformations in MTH by operando UV-Raman spectroscopy.

Molecular elucidating of an unusual growth mechanism for polycyclic aromatic hydrocarbons in confined space

“…Nevertheless, this method is limited to the analysis of molecules with maximum molar weight below 300 g mol −1 , due to the decreased solubility with increasing size of PAHs 5 . Various sophisticated spectroscopic techniques such as infrared spectroscopy 6 , UV-Raman spectroscopy [7][8][9] , UV-Vis spectroscopy 10 , and 13 C nuclear magnetic resonance (NMR) spectroscopy [11][12][13] , with the merits of being nondestructive and operable in situ or operando modes, have also been extensively used. These spectroscopic techniques are capable of differentiating the insoluble, highly condensed PAHs from the soluble, light constituents, yet, they fail in determining the molecular structure of the insoluble fraction of coke 14 .…”

Operando UV-Raman study of the methanol to olefins reaction over SAPO-34: Spatiotemporal evolution monitored by different reactor approaches

“…Concerning the assignment of the observed UV-Raman signals, the concerted intensity trend suggests that the bands at 1635 cm -1 , 1560 cm -1 and 1415 cm -1 are related to the same or same group of chemical species. These can be related to alkenes [22,42]: this assignment is supported by the known retention of C4+ alkenes within the cages of SAPO-34, since the small 8-memeberd windows do not allow them to out-diffuse from framework [43]. The 1600 cm -1 is assigned to the G band of amorphous carbon, whereas the usually observed D band is suppressed due the use of UV excitation in its measurement [24].…”

“…roughly the double of ones of pure PAHs), indicating the overlap of the features of more than a single molecule. Furthermore, according to dissolution-extraction experiment performed on the same catalyst [8] and to modelling results [22], these PAHs are most probably methylated and their skeletal vibration can be affected by such substitutions. The more abundant presence of PAHs at early TOS (according to the larger intensity of the 1370 cm -1 band) is further supported by the observed lower frequency of the most intense, band at about 1625 cm -1 : this frequency is characteristic for the small PAHs listed above.…”

“…operando) conditions [10][11][12][13][14][15][16][17][18][19][20]. To tackle both of the aforementioned challenges, Raman spectroscopy has a considerable potential, but the number of literature reports dealing with the investigation of deactivation during MTH is still limited in comparison to other tools [10,11,13,14,21,22]. The advantages of Raman spectroscopy mostly relate to its capability in distinguishing among the several allotropic forms of carbon [23,24].…”

“…Among the proposed test cases, this setup has been applied to the study of MTH over ZSM-5 and ZSM-22. Recently, we successfully exploited the same setup in the operando UV-Raman investigation of hydrocarbons transformations occurring during MTH as a function of the topology of different zeolite catalysts [22]. Aiming to overcome some of the limitation of the previous devices (mostly related to the instability of the focus over the sample upon fluidization), some of us recently developed a mechanical-based setup, where the movement is produced through a magnetic stirring [34,35].…”