In operando

The main inconvenient of this methodology is that the results cannot be considered stricto sensu as obtained in operando conditions, because the system was perturbed from the steady state to reveal hidden species. It could be even hypothesized that such compounds are uniquely due to the particular test conditions and not to the real reaction pathway. A method to discard such kind of criticism is to maintain the chemical steady state of the reaction, while introducing a perturbation via a sudden exchange of one... 

Topspe, H. (2003) Developments in operando studies and in situ characterization of heterogeneous catalysts, J. Catal., 216, 155. 

Lercher and coworkers studied xylene isomerization on surface modified HZSM-5 zeolites [133]. They used time-resolved in situ IR spectroscopy to monitor the concentration of reactants and product inside the pores of the zeolite. Massiani and coworkers studied the conversion of xylene over mordenites [134]. They used in operando IR to characterize the adsorbed surface species and evolution of the active sites as the reaction proceeded. 

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. 

Dupont and van Leeuwen studied hydroformylation reactions in [bmim]PF6 [63] and observed the formation of catalytically active rhodium species in operando (Fig. 13). The same class of reaction has been studied again by Dupont, this time in the IL [bmim]Tf2N [64]. Here, they reported H/D exchange in the 2-position of the imidazolium ring of the IL, especially in the presence of a base - a finding that has been reported earlier already ([3,9], and references therein). The involvement of A-heterocyclic carbene species was discussed but not proven. 

Powder diffraction is very well suited for studies at non-ambient conditions. Naturally, one of the early applications of powder diffraction was high temperature studies of phase transformations. Development of equipment for low temperature and high-pressure studies quickly followed. Later, application of powder diffraction for in situ, time-resolved and in operando studies were successfully pursued. 

We have not made any distinction between in situ and in operando experiments. In operando requires the system studied to be under identical conditions as in, for example, an industrial process, while in situ could describe simulated conditions such as time-resolved studies of synthesis and chemical reactions. 

Bruckner, A. (ed) (2010) Recent developments in operando spectroscopy. Catal. Today, 155, 155-330. 

Recent Trends in Operando and In Situ Characterization Techniques for Rationai Design ofCataiysts... 

Richey, F. W., C. Tran, V. Kalra, and Y. A. Elabd. 2014. Ionic liquid dynamics in nanoporous carbon nanofibers in supercapacitors measured with in operando infrared spectroelectrochemistry. Journal of Physical Chemistry C 118 21846—21855. 

FIGURE 4.19 In operando infrared spectroelectrochemical results initialized time-resolved concentration (concentration units g/g corresponds to gpMiMiiTFsi/geiectrode) of the EMIM cation and TFSI anion in NCNFs during three CV at 20 mV s from (a) 0-1 V, (b) 0-1.5 V, and (c) 0-2 V. (d) Illustration showing ion adsorption within nanopores of NCNFs. (Reprinted with permission from Richey, F. W. et al., Ionic liquid dynamics in nanoporous carbon nanofibers in supercapacitors measured with in operando infrared spectroelectrochemistry. The Journal of Physical Chemistry C 118, 21846-21855. Copyright 2014 American Chemical Society.)... 

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