Operando techniques

Tibiletti, D., Goguet, A., Reid, D. et al. (2006) On the need to use steady-state or operando techniques to investigate reaction mechanisms An in situ DRIFTS and SSITKA-based study example, Catal. Today, 113, 94. 

Tinnemans, S.J., Mesu, J.G., Kervinen, K. el al. (2006) Combining operando techniques in one spectroscopic-reaction cell New opportunities for elucidating the active site and related reaction mechanism in catalysis, Catal. Today, 113, 3. 

Operando methodology aims to define and characterize structure/function relationships which must be interfaced with rate and dynamics measurements of the elementary steps. Recent years have shown a marked increase in the presence of spectroscopic investigations of catalytic reactions in literature (see Catalysis Today, 113 issues 1-2). For example, operando techniques were used to determine the temperature stability range of two NOx reduction catalyst types, (NH4)[Co(H20)2]Ga(P04)3 vi. (NH4)[Mn(H20)2]Ga(P04)3. Fig. 5 shows that the catalyst with manganese changes in structural stability around 673 K. Inspection of the catalyst with cobalt shows that there is no structure modification at a temperature below 673 K. 

It has been quickly recognized that the individual operando techniques can be combined to yield a more complete picture of the catalytic reaction sequence. In addition, since many reactions of industrial significance occur in the liquid phase, it is important that techniques are developed to probe and monitor those systems under conditions that at least keep the reactants, intermediates and products in their actual operating states or phases. This has resulted in researchers utilizing a multitude of techniques, some in situ and ex situ, to obtain a more complete understanding of the entire catalytic cycle. 

Itmumerable mechanistic studies of alcohol oxidation on Pt-based electrocatalysts in acidic media have been published over the last few years. Methanol, " ethanol ° and ethylene glycol have been the most studied substrates and their oxidation paths on Pt or Pt alloys have been substantiated using a variety of in situ, extra situ and operando techniques as well as quantum mechanical calculations. The experimental techniques include reflection IR spectroscopy (IR), surface enhanced IR asbsorption spectroscopy (SEIRAS), " attemrated total reflection-IR absorption spectroscopy (ATR-IRAS), differential electrochemical mass spectroscopy (DEMS), single potential alteration IR spectroscopy... 

The other technique we use under operando conditions is infrared spectroscopy, which has also been used in catalysis research for more than 50 years. The new surname as an operando technique makes it sound more glamorous, but it is really an additional qualifier for in situ IR, which has been around for decades. In fact, the editor of this book, John Regalbuto, did his Ph.D. work using in situ and operando... 

The results presented in this case show that the effect of sulfur on Pt catalysts during CO oxidation is a dynamic phenomena that strongly depends on the catalyst s history, including (1) how sulfur is added, (2) the pretreatment used before reaction, (3) the type of support used, (4) crystallite size, (5) the reaction conditions, and (6) the time on stream at which measurements are made. The results show how critical is the use of operando techniques to correlate the state of the surface with the catalytic activity. 

Owing to the complex architecture of the fuel cell and especially the presence of a flow field and gas diffusion layer, only a few spectroscopic operando techniques are available. The most powerful ones include the use of X-rays, which to a certain extent may penetrate through the above-mentioned carbon materials. One of these techniques, XAS, is very useful in this respect since it provides information about catalyst structure, electronic properties [107-110], and, in certain cases, surface species on these catalyst nanoparticles [30]. Several spectroscopic test cells have been proposed [109, 110], one of which was demonstrated recently to allow for in situ investigation of fuel cell catalysts without any compromise regarding cell design [111]. Another useful X-ray technique is XRD, which has recently been applied successfully to monitor oscillations in particle growth on Pt/C catalysts [112]. 

The development of in situ or operando techniques (infrared (IR), Raman, UV-vis) to investigate working heterogeneous catalysts in gas-phase reactions has flourished over the last decade. It is state-of-the-art to couple several of these methods at... 

Aldana, P.A.U Ocampo, R Kobl, K. Louis, B. Starzyka, F. T.- Daturi, M. Bazin, R Thomas, S. Roger, A.C. Catalytic CO Valorization into CH on Ni-Based Ceria-Zirconia. Reaction Mechanism by Operando Techniques, 2013, 215, 201-207. 

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