Operando Raman spectroscopy

In Situ and Operando Raman Spectroscopy of Oxidation Catalysts... 

It was shown recently, by operando RAMAN spectroscopy, that the primary coke species formed in/on SAPO-34 were mainly polyolefmic, some aromatic species were present on ZSM-5, and mainly polyaromatic or substituted aromatic species were predominant in USY at high temperatures [225],... 

Guerrero-Perez, M.O. and Banares, M.A. (2006) From conventional in situ to operando studies in Raman spectroscopy, Catal. Today, 113, 48. 

Bruckner, A. and Kondratenko, E. (2006) Simultaneous operando EPR/UV-vis/laser-Raman spectroscopy - A powerful tool for monitoring transition metal oxide catalysts during reaction, Catal. Today, 113, 16. 

Many of the characterization techniques described in this chapter require ambient or vacuum conditions, which may or may not be translatable to operational conditions. In situ or in opemndo characterization avoids such issues and can provide insight and information under more realistic conditions. Such approaches are becoming more common in X-ray adsorption spectroscopy (XAS) methods ofXANES and EXAFS, in NMR and in transmission electron microscopy where environmental instruments and cells are becoming common. In situ MAS NMR has been used to characterize reaction intermediates, organic deposits, surface complexes and the nature of transition state and reaction pathways. The formation of alkoxy species on zeolites upon adsorption of olefins or alcohols have been observed by C in situ and ex situ NMR [253]. Sensitivity enhancement techniques play an important role in the progress of this area. In operando infrared and RAMAN is becoming more widely used. In situ RAMAN spectroscopy has been used to online monitor synthesis of zeolites in pressurized reactors [254]. Such techniques will become commonplace. 

Bruckner A. Killing three birds with one stone - simultaneous operando EPR/UY-vis/ Raman spectroscopy for monitoring catalytic reactions. Chem Commun. 2005 1761. 

Over the past two decades, Raman spectroscopy has been extensively applied during catalytic oxidation reactions by mixed-metal oxides and metals under in situ and operando spectroscopy conditions, which has allowed the direct identification of the catalytic active sites involved in the oxidation reactions. Among the multiple spectroscopic techniques that can provide information about the catalytic active sites under oxidation reaction conditions, Raman spectroscopy is unique because of its ability to directly provide molecular level information that allows discrimination among the different catalytic active sites which may be present in the oxidation catalyst. This chapter provides a snapshot of the types of fundamental information obtainable by Raman spectroscopy, and the different types of catalytic materials and oxidation reactions that have been reported, especially under oxidation reaction conditions. 

The oxidation and ammoxidation of propylene (H2CHC = CH3) to acrolein (H2CHC = CHO) and acrylonitrile (H2CHC = CN) respectively, constitute major chemical intermediates. Conversion of propylene to acrolein is conducted in an oxidising environment, while conversion of propylene to acrylonitrile requires both molecular O2 and NH3. The industrial catalyst employed for these oxi-dation/ammoxidation reactions is a bulk Bi-Mo-0 mixed oxide. The alpha-Bi2 (M0O4) 3 phase is one of the most active phases and its Raman spectrum is shown in Fig. 17.7. An operando Raman-GC spectroscopy investigation of propylene... 

Figure 19.2. Experimental set-ups for (a) simultaneous operando EPR/UV-vis/Raman spectroscopy (adopted from Ref. 15) and (b) simultaneous DRIFTS/UV-vis spectroscopy.

Bruckner, A. (2005). Killing Three Birds with One Stone - Simultaneous Operando EPR/UV-Vis/Raman Spectroscopy for Monitoring Catalytic Reactions, Chem. Commun.,13,... 

Banares, MA., Guerrero-Perez, M.O., Eieno, J.L.G., and Cortez, G.G. Raman spectroscopy during catalytic operations with on-hne activity measurement (operando spectroscopy) A method for understanding the active centres of cations supported on porous materials. 7 Mater. Chem. 2002, 12, 3337-3342. 

Wachs, I.E. In situ Raman spectroscopy of catalysts past, present and future. In Proceedings 2nd International Congress on Operando Spectroscopy, Lunteren The Netherlands, March 2-6, 2003, p. 30. 

In situ or operando studies preferentially combine the identification of the structure and the catalytic performance. This is a demanding task and cannot be realized without compromises [31-34], For X-ray-based techniques and UY-vis, Raman, or IR spectroscopy, the reactor needs windows where the light can shine through or a design so that NMR/EPR studies can become possible. The principle is given in Figure 4.3.5. 

Beale AM, van der Eerden AMJ, Kervinen K, Newton MA, Weckhuysen BM. Adding a third dimension to operando spectroscopy a combined UV-Vis, Raman and XAFS setup to study heterogeneous catalysts under working conditions. Chem Commun. 2005 3015. 

Brandhorst M, Cristol S, Capron M, et al. Catalytic oxidation of methanol on M0/AI2O3 catalyst an EPR and Raman/infrared operando spectroscopies study. Catal Today. 2006 113 34. 

Another important process in which catalyst deactivation by coke deposits plays an important role is propane dehydrogenation, which can be performed with a variety of materials, including metal and metal oxide catalysts. Different in situ and operando spectroscopies have been applied to these catalysts, including UV-vis, Raman, electron paramagnetic resonance (EPR), and X-ray absorption spectroscopies [4, 115, 140],... 

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