Situ Characterization

Surface science studies of corrosion phenomena are excellent examples of in situ characterization of surface reactions. In particular, the investigation of corrosion reactions with STM is promising because not only can it be used to study solid-gas interfaces, but also solid-liquid interfaces. 

Characterization of zeolites is primarily carried out to assess tire quality of materials obtained from syntliesis and postsyntlietic modifications. Secondly, it facilitates tire understanding of tire relation between physical and chemical properties of zeolites and tlieir behaviour in certain applications. For tliis task, especially, in situ characterization metliods have become increasingly more important, tliat is, techniques which probe tire zeolite under actual process conditions. 

Analysis of stress distributions in epitaxial layers In-situ characterization of dislocation motion in semiconductors Depth-resolved studies of defects in ion-implanted samples and of interface states in heterojunctions. 

Scanning electrochemical microscopy can also be applied to study localized biological activity, as desired, for example, for in-situ characterization of biosensors (59,60). In this mode, the tip is used to probe the biological generation or consumption of electroactive species, for example, the product of an enzymatic surface reaction. The utility of potentiometric (pH-selective) tips has also been... 

The two processes are becoming closer in concept. For instance, MOCVD is using techniques developed for MBE such as in situ characterization monitoring, load lock, and lower pressure levels, and MBE is now using chemical sources such as organome-tallics, which are typical of CVD. 

For the in situ characterization of modified electrodes, the method of choice is electrochemical analysis by cyclic voltammetry, ac voltammetry, chronoamperometry or chronocoulometry, or rotating disk voltametry. Cyclic voltammograms are easy to interpret from a qualitative point of view (Fig, 1). The other methods are less direct but they can yield quantitative data more readily. 

X-ray absorption spectroscopy was used for situ characterization of active, supported Pt catalysts. 

Despite the success in modeling catalysts with single crystals and well defined surfaces, there is a clear need to develop models with higher levels of complexity to address the catalytically important issues specifically related to mixed oxide surfaces. The characterization and design of oxide surfaces have not proven to be easy tasks, but recent progress in identification of the key issues in catalytic phenomena on oxide surfaces by in-situ characterization techniques on an atomic and molecular scale brings us to look forward to vintage years in the field. 

The latter report demonstrated the unique ability of this technique to resolve surface structure as well as surface composition at the electrified solid-liquid interfaces. In particular, STM has become an important tool for ex situ and in situ characterization of surfaces at the atomic level, in spite its significant limitations regarding surface composition characterization for bimetallic systems, such as the lack of contrast for different elements and the scanned surface area being too small to be representative for the entire surface. To avoid these limitations, STM has been mostly used as a complementary tool in surface characterization. 

As the reader might have noticed, many conclusions in electrocatalysis are based on results obtained with electrochemical techniques. In situ characterization of nanoparticles with imaging and spectroscopic methods, which is performed in a number of laboratories, is invaluable for the understanding of PSEs. Identification of the types of adsorption sites on supported metal nanoparticles, as well as determination of the influence of particle size on the adsorption isotherms for oxygen, hydrogen, and anions, are required for further understanding of the fundamentals of electrocatalysis. 

Complementary in-situ characterization of the surface species using infrared (IR) spectroscopy has provided information on the identity and coverage of the surface species involved in the NO catalytic reduction [56]. It was found that the changes observed in the surface coverages of NO and CO correlate well with the observed changes in N20 selectivity mentioned above below 635 K, where N20 formation is favored, NO is the major adsorbate on the surface, whereas above 635 K, where N2 formation is preferred,... 

Le Bourdon, G., Adar, F., Moreau, M. et al. (2003) In situ characterization by Raman and IR vibrational spectroscopies on a single instrument deNO, reaction over a Pd/y-Al203 catalyst, Phys. Chem. Chem. Phys., 5, 4441. 

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

The metallic component of HCK catalysts provides hydrogenation, dehydrogenation, hydrogenolysis, and isomerization. The number and nature of reactive hydrogen species created by the interaction of a bifunctional catalyst with hydrogen is not well understood [103], on the other hand, neither the action of those species on the catalytic sites is understood. The main limitation in this understanding is the dynamic character of the interaction however, now that in situ characterization techniques are becoming available, research would soon defeat the limitations. 

Pemberton J.E. in Electrochemical Interfaces. Modem Techniques for In-Situ Characterization, Abruna H.D. ed., VCH Verlag Chemi, Berlin, 1991. 

Ducreux, O., Lynch, J., Rebours, B., Roy, M., and Chaumette, P. 1998. In situ characterization of cobalt based Fischer-Tropsch catalysts A new approach to the active phase. Stud. Surf. Sci. Catal. 119 125-30. 

Bimetallic (98) and alloy catalysts (97), of interest for hydrogenation reactions, have been investigated in in situ characterizations of methanol synthesis from CO and H2 in the presence of novel Cu-Pd alloy catalysts supported on carbon the results show surface segregation of palladium on the catalyst particles in CO atmospheres, but surfaces with equal amounts of copper and palladium when the atmosphere is H2 (97). 

In situ Characterization of Langmuir-Blodgett Films by using a Quartz Crystal Microbalance as a... 

We review useful usages of a quartz crystal-microbalnce (QCM) as tool of in situ characterization of Langmuir-Blodgett (LB) films transfer ratio and water incorporation during a transfer process, swelling behavior in water subphase, and detachment at the air-water interface. 

In situ characterization. Catalysts should preferably be investigated under the conditions under which they are active in the reaction. Various reasons exist why this may not be possible, however. For example, lattice vibrations often impede the use of EXAFS, XRD and Mossbauer spectroscopy at reaction temperatures the mean free path of electrons and ions dictates that XPS, SIMS and LEIS are carried out in vacuum, etc. Nevertheless, one should strive to choose the conditions as close as possible to those of the catalytic reaction. This means that the catalyst is kept under reaction gases or inert atmosphere at low temperature to be studied by EXAFS and Mossbauer spectroscopy or that it is transferred to the vacuum spectrometers under conditions preserving the chemical state of the surface. 

We have recently modified U7) one of the several radiochemical methods (U5) which have been used for surface electrochemistry investigations in order to characterize adsorption on well-defined, single crystal electrodes. Below, we will describe the technique and identify some challenging issues which we will be able to address. The proposed method is sensitive to a few percent of a monolayer at smooth surfaces, is nondestructive and simple to use. The radiochemical measurements can be made with all compounds which can be labelled with reasonably long-lived, preferably g- emitting radioisotopes. We believe this technique will fulfill the quantitative function in in situ surface analysis as Auger spectroscopy currently does in vacuum, ex situ characterization of electrodes. 

Vibrational spectroscopy techniques are quite suitable for in situ characterization of catalysts. Especially infrared spectroscopy has been used extensively for characterization of the electrode/solution interphases, adsorbed species and their dependence on the electrode potential.33,34 Raman spectroscopy has been used to a lesser extent in characterizing non-precious metal ORR catalysts, most of the studies being related to characterization of the carbon structures.35 A review of the challenges and applications associated with in situ Raman Spectroscopy at metal electrodes has been provided by Pettinger.36... 

B.H. Cumpston, I.D. Parker, and KF. Jensen, In situ characterization of the oxidative degradation of a polymeric light emitting devices, J. Appl. Phys., 81 3716-3720, 1997. 

Conversion of methanol and ethanol on H-ZSM-5 zeolite The first in situ characterization of the adsorbed species on this catalyst has been reported for the conversion of methanol and ethanol to hydrocarbons (6 ). ... 

X-ray photoelectron spectroscopy is indeed quite informative, but requires the use of expensive instrumentation. Also, the detection of photoelectrons requires the use of ultrahigh vacuum, and therefore can mostly be used for ex situ characterization of catalytic samples (although new designs are now available for in situ studies [146,147]). Finally, XPS probes the upper 10 to 100 A of the solid sample, and is only sensitive to the outer surfaces of the catalysts. This may yield misleading results when analyzing porous materials. 

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