A Novel Raman Setup Based on Magnetic-Driven Rotation of Sample

Abstract

The Raman characterization of catalysts (as for any material) is generally a difficult task, since the numerous drawbacks affecting this technique, e.g. overlapping with photoemission phenomena and excitation induced sample damaging. These side effects are detrimental toward advanced applications of Raman spectroscopy, as in situ and/or operando ones. If photoemission can be often avoided by changing the excitation wavelength, the sample damaging requires to take advantage of specific tools, developed ad hoc. The aim of this work is to show the potentialities of a novel Raman setup, specifically designed for the in situ study of catalytic materials, where the sample is moved by means of a magnetic-driven sample-holder), reducing the excitation induced damaging to a negligible extent. Various examples related to catalysis field (involving inorganic, organic and mixed systems) are reported to support this statement.

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

“…Nevertheless, the application of UV-Raman spectroscopy in the MTH reaction has been very limited because of possible sample damaging under the intense UV light which requires special reactor systems. [30][31][32][33][34] Li and Stair were the first to apply UV-Raman spectroscopy to study the formation of coke over ZSM-5, SAPO-34 and USY during the conversion of methanol to olefins. 31,32 The authors reported that for SAPO-34 the coke species are mainly of polyolefinic nature.…”

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

“…The magnetic stirring setup (Figure 2a) is derived from the house-made cell described in ref. [34,35], originally developed for ex situ studies [8,36,37], and is a simple U-shaped quartz-glass reactor, where a portion of the inlet channel is an optical grade quartz cuvette, allowing the measurement of UV-Raman spectra. Furthermore, with respect to the parent cell, two external electrical heating elements are placed on the sides of the cuvette, allowing to span the 50-500 °C temperature range.…”

“…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]. The latter has been exploited in a carefully controlled study of some relevant molecular species taking part to the deactivation in MTH (i.e.…”

Toward a novel framework for bloodstains dating by Raman spectroscopy: How to avoid sample photodamage and subsampling errors

“…And that is because providing a representative Raman signature, which in case of singlepoint measurements can be only obtained by performing multiple measurements across the sample, is hardly possible within short space of time. Fortunately, the problem of laser power and interconnected time resolution can be mitigated by a relatively simple solution applied in this study -implementation of rotating measurement mode [13,14]. Since in this case the irradiated point of the bloodstain is being constantly refreshed, the excitation energy is distributed over a larger area, hence the risk of sample damaging can be significantly reduced.…”

“…In view of the above, this study intended to expand the current Raman-based approaches largely through eradication of the risk of the laser-induced degradation of bloodstains [3,9,12] and subsampling errors. In order to do so, the rotating measurement mode that involved spinning the bloodstain sample during the spectral acquisition by means of a magnetic-driven sample-holder [13,14] was established, and subsequently employed for characterizing the behaviour of bloodstains during three-week degradation period. To verify the capability of the novel sampling method to provide data that facilitated discerning differently-aged blood traces, its performance was compared with the routinely applied single-point sampling procedure (the static mode).…”