Spectroscopic Reactors and Practical Aspects

For the sake of completeness, some more unusual techniques for studying catalytic reactions should also be described, which enable monitoring of changes in sohd particles such as phase transformations and crystallization [24-26]. This could be of interest for heterogeneously catalyzed reactions, too, because coupling with spectroscopic methods, such as Raman, ATR-FTIR, and UV-vis, can provide more detailed structural information. 

Su et al. [24] studied the polymorphic transformation of n-mannitol by in situ Raman spectroscopy coupled with FBRM (focused beam reflectance measurement) and PVM (particle vision measurement). In this way, relationships between fine particles and metastable-form dissolution, and also between coarse particles and stable-form crystallization, could be defined. The different polymorphs were identified by Raman spectroscopy. FBRM provided a method for independently verifying these observations. PVM, in turn, verified the data interpretation strategy employed for FBRM. 

Hao et al. [25] used the same setup, but extended by ATR-FTIR spectroscopy, to study the enantiotropic transformation of p-aminobenzoic acid polymorphs. Raman spectroscopy was used to monitor the solid-phase concentration, whereas the liquid-phase concentration was monitored by ATR-FTIR spectroscopy. Particle size and morphology were examined by FBRM and PVM. 

A similar method to PVM and FBRM is BVI (bulkvideo imaging), wherein a video camera is used through an observation window of the reaction vessel or a process endoscope employed. Simon et al. [26] used this technique coupled with UV-vis spectroscopy, FBRM, and calorimetry to monitor the crystallization of caffeine and palm oil. UV-vis spectroscopy and calorimetry were used for validation. BVI was shown to detect the boundaries of the metastable zone with comparable or better performance than FBRM and UV-vis probes. 

The crucial point in realizing a multiple technique approach for elucidating catalytic reaction mechanisms, and studying catalysts at work, is achieving an appropriate 

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