Surface characterization spectroscopic methods

While in situ techniques encompass all characterization/spectroscopic methods that can be used to probe the surface chemistry of an operating practical catalyst, its entirety is too large to cover in any real detail. Therefore the methods covered in this review were chosen based on their prevalence and use in the field and the potential for significant observations during reaction cycles. Some methods, such as ATR, TAP and catalytic shock tube, were chosen based on the potential of these methods and the likelihood that they will become more widely used as they are integrated with evolving spectroscopic techniques. 

Similarly, several works can be cited on cationic SIP on flat substrates. Again, the advantage of cationic SIP is that it puts at one s disposal surface-sensitive spectroscopic methods that allow successful in situ characterization of polymer brushes on surfaces ... 

NEXAFS is a synchrotron-based spectroscopic tool routinely used as a complementary technique with XPS for surface characterizations. This method probes the adsorption of X-rays by the excitation of core (K-shell) electrons into unoccupied electronic states near the ionization limit. Subsequent emission of Auger electrons results in the formation of an NEXAFS electron yield the observed spectmm. Because the source of Auger electrons can extend only up to 10 nm and the spectral peak positions and intensities are directly related to the nature of unoccupied electronic states, NEXAFS spectroscopy provides an important tool for studying stmctural and chemical features of various surface thin films and coatings (Hemraj-Benny et al., 2006 Hahner, 2006). 

Science relies on the development of new techniques in order to make new measurements and gain new insights. While the measurements have always been my priority, rather than the techniques, there was often the need to develop or improve certain methods along the way. The high-pressure-low-pressure apparatus, as described above (3.1, 3.2) enabled catalytic reactions to be carried out at pressures up to a hundred atmospheres, and to be followed by UHV surface characterization, by methods such as XPS, HREELS, LEED and mass spectroscopic measurements, without exposure to the air. This was a significant achievement within the Somorjai group, since it at least partially addressed the pressure gap , between UHV surface science and experiments carried out in catalytic reactors (5.6). 

Besides synthesis, current basic research on conducting polymers is concentrated on structural analysis. Structural parameters — e.g. regularity and homogeneity of chain structures, but also chain length — play an important role in our understanding of the properties of such materials. Research on electropolymerized polymers has concentrated on polypyrrole and polythiophene in particular and, more recently, on polyaniline as well, while of the chemically produced materials polyacetylene stih attracts greatest interest. Spectroscopic methods have proved particularly suitable for characterizing structural properties These comprise surface techniques such as XPS, AES or ATR, on the one hand, and the usual methods of structural analysis, such as NMR, ESR and X-ray diffraction techniques, on the other hand. 

Enzymes that catalyze redox reactions are usually large molecules (molecular mass typically in the range 30-300 kDa), and the effects of the protein environment distant from the active site are not always well understood. However, the structures and reactions occurring at their active sites can be characterized by a combination of spectroscopic methods. X-ray crystallography, transient and steady-state solution kinetics, and electrochemistry. Catalytic states of enzyme active sites are usually better defined than active sites on metal surfaces. 

Busca, G. (1999) The surface acidity of solid oxides and its characterization by IR spectroscopic methods. An attempt at systematisation, Phys. Chem. Chem. Phys., 1, 723. 

Wakabayashi, F. and Domen, K. (1997) A new method for characterizing solid surface acidity - an infrared spectroscopic method using probe molecules such as N2 and rare gases. Catalysis Surveys from Japan 1 181. 

A complete review of spectroscopic methods applied to the analysis of alkyl-modified surfaces with a comprehensive list of spectroscopic indicators of alkyl chain conformational order is provided elsewhere [9] this review will focus on the application of spectroscopic and other relevant experimental techniques for the characterization of shape-selective chromatographic materials. On the whole, it has been observed experimentally that any increase in alkyl stationary-phase conformational order promotes an increase in selectivity for shape-constrained solutes in RPLC separations [9], As a complement to the wealth of spectroscopic and chromatographic data, the use of molecular simulation techniques to visualize and characterize alkyl-modified surfaces may also provide new insights into molecular-level features that control shape selectivity. A review of progress in the field of chromatographic material simulations will also be discussed. 

In the next sections we introduce some of the most important experimental techniques of surface characterization. For the interested reader, a broad range of books on this topic is available (e.g. Refs. [346,347]). We start by discussing microscopy, continue with diffraction, and finally focus on spectroscopic methods. 

A catalyst surface may be assumed to be characterized by specific poisoning if the number of adsorption sites, the strength (or the strength distribution) of the adsorbate-catalyst interaction, and the nature of this interaction as well as the chemical nature of the adsorbed species can be determined. All three properties are equally important to characterize fully, i. e., qualitatively and quantitatively, a catalyst surface. The number of adsorption sites may be determined from the adsorbed amount of poison as measured by conventional techniques, whereas thermoanalytical methods have to be applied for a quantitative characterization of the adsorption bond strength. Spectroscopic methods will be most suitable for studies of the chemical nature of the adsorbed species and the nature of the adsorbate-surface interaction. 

Mesoporous silica materials with hierarchical tubule-within-tubule structures have been prepared and characterized by spectroscopic methods.97 Strong photoluminescence of these materials is explained as due to the presence of Si-OH complexes located on the nanotube surface, which also explains the persistence of the signal for some time after the pumping laser is turned off. 

A new spectroscopic method for the characterization of surface vacancy clusters is a combination of positron lifetime spectroscopy, which determines the size of vacancy clusters, and coincidence Doppler broadening of annihilation radiation, which gives information on where vacancy clusters are located [5, 6]. If these clusters are located on the surface of gold nanoparticles, namely the interface between the particle and host matrix, the surroundings of the clusters should include both particle atoms and the matrix atoms. Doppler broadening of annihilation radiation (DBAR) with two-detector coincidence should be able to reveal these atomic constituents, and therefore elucidate the location of vacancy clusters. 

---