X-ray adsorption spectroscopy

It has been observed that cobalt may undergo large-scale reconstruction under a synthesis gas environment.27 Reconstruction is a thermodynamically driven process that results in the stabilization of less reactive surfaces. Recent molecular modeling calculations have shown that atomic carbon can induce the clock reconstruction of an fee cobalt (100) surface.28 It has also been postulated and shown with in situ x-ray adsorption spectroscopy (XAS) on cobalt supported on carbon nanofibers that small particles (<6 nm) undergo a reconstruction during FTS that can result in decreased activity.29... 

V has been elucidated by x-ray adsorption spectroscopy [5]. Gold has an fee lattice, and the Au(lll) surface forms a triangular lattice with a lattice constant of 2.89 A. Copper atoms are smaller than gold atoms, and they adsorb in the threefold hollow sites (see Fig. 4.12), forming a triangular lattice commensurate with that of the substrate ... 

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. 

Weesner, E.J. and Bleam, W.F., Binding characteristics of Pb + on anion-modified and pristine hydrous oxide surfaces studied by electrophoretic mobility and X-ray adsorption spectroscopy, J. Colloid Interf. Sci., 205, 380, 1998. 

The strain in the deposited platinum layers was measured by low-energy electron diffraction (LEED), as shown in Fig. 18.8a. An increase of the thickness of Pt layers resulted in decreased strain, indicating that the strain was relaxing in the Pt layers. Meanwhile, we have used X-ray emission spectroscopy (XES) and X-ray adsorption spectroscopy (XAS) to probe the occupied and unoccupied portion of the Pt-projected d bands, as illustrated in Fig. 18.8b. The sketch of Fig. 18.8c on left... 

The electrochemical results correlated with in situ X-ray adsorption spectroscopy that provides information on the electronic and geometric factors show that the alloys have higher Pt 5d-orbital vacancies and shorter Pt-Pt distances and that inhibit the chemisorptions of OH on the platinum facilitating faster oxygen reduction. 

He also made an important contribution to the background of novel diagnostic methods, such as description of the local current distribution around a Pt-free spot in the PEFC anode, a key problem for transmission x-ray adsorption spectroscopy of the fuel cell cathode. He filed many patents based on his theoretical work. 

The catalysts studied were characterized using X-ray powder diffraction (XRD), X-ray fluorescence analysis (XFA), transmission electron microscopy (TEM), X-ray adsorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and hquid nitrogen physisorption methods. 

XANES X-ray adsorption nearedge spectroscopy [178a] Same as NEXAFS Same as NEXAFS... 

High quahty SAMs of alkyltrichlorosilane derivatives are not simple to produce, mainly because of the need to carefully control the amount of water in solution (126,143,144). Whereas incomplete monolayers are formed in the absence of water (127,128), excess water results in facile polymerization in solution and polysiloxane deposition of the surface (133). Extraction of surface moisture, followed by OTS hydrolysis and subsequent surface adsorption, may be the mechanism of SAM formation (145). A moisture quantity of 0.15 mg/100 mL solvent has been suggested as the optimum condition for the formation of closely packed monolayers. X-ray photoelectron spectroscopy (xps) studies confirm the complete surface reaction of the —SiCl groups, upon the formation of a complete SAM (146). Infrared spectroscopy has been used to provide direct evidence for the hiU hydrolysis of methylchlorosilanes to methylsdanoles at the soHd/gas interface, by surface water on a hydrated siUca (147). 

The prepared catalysts were characterized by x-ray diffraction (XRD), N2 adsorption and CO chemisorption. Also, X-ray absorption spectroscopy (XAS) at the Ni K edge (8.333 keV) of reference and catalyst samples was carried out in the energy range 8.233 to 9.283 keV at beamline X18B of the... 

Elder, R.C., Tepperman, K.G., Eidsness, M.K., Heeg, M.J., Shaw, C.F. Ill and Schaeffer, N. A. (1983) Gold-based antiarthritic drugs and metabolites. Extended x-ray adsorption fine structure (EXAFS) spectroscopy and x-ray absorption near edge spectroscopy (XANES). ACS Symposium Series, 209, 385-400. 

X-ray photoemission spectroscopy and X-ray absorption spectroscopy demonstrated that the mixed film can be precisely adjusted by the composition of the solution used for co-adsorption of C12 and TMPP. The monolayer formed from the C12/TMPP = 1/10,000molmol solution contains only TMPP moieties, while that from the 1/ 1000 solution is mostly TMPP with a few percent of C12. The monolayer formed from the 1/100 solution contains a minor amount of TMPP, and that from the 1/10 solutions consists exceptionally of Cl 2 moieties [18]. 

TeUskaM, O Grady WE, RamakerDE. 2004. Determination of H adsorption sites on Pt/C electrodes in HCIO4 from Pt L23 X-ray absorption spectroscopy. J Phys Chem B 108 2333-2344. 

The pros and cons of oxidative dehydrogenation for alkene synthesis using doped cerianites as solid oxygen carriers are studied. The hydrogen oxidation properties of a set of ten doped cerianite catalysts (Ce0.9X0.1Oy, where X = Bi, In, La, Mo, Pb, Sn, V, W, Y, and Zr) are examined under cyclic redox conditions. X-ray diffraction, X-ray photoelectron spectroscopy, adsorption measurements, and temperature programmed reduction are used to try and clarify structure-activity relationships and the different dopant effects. 

Gomez-Sainero et al. (11) reported X-ray photoelectron spectroscopy results on their Pd/C catalysts prepared by an incipient wetness method. XPS showed that Pd° (metallic) and Pdn+ (electron-deficient) species are present on the catalyst surface and the properties depend on the reduction temperature and nature of the palladium precursor. With this understanding of the dual sites nature of Pd, it is believed that organic species S and A are chemisorbed on to Pdn+ (SI) and H2 is chemisorbed dissociatively on to Pd°(S2) in a noncompetitive manner. In the catalytic cycle, quasi-equilibrium ( ) was assumed for adsorption of reactants, SM and hydrogen in liquid phase and the product A (12). Applying Horiuti s concept of rate determining step (13,14), the surface reaction between the adsorbed SM on site SI and adsorbed hydrogen on S2 is the key step in the rate equation. 

Electrochemical impedance spectroscopy was used to determine the effect of isomers of 2,5-bis( -pyridyl)-l,3,4-thiadiazole 36 (n 2 or 3) on the corrosion of mild steel in perchloric acid solution <2002MI197>. The inhibition efficiency was structure dependent and the 3-pyridyl gave better inhibition than the 2-pyridyl. X-ray photoelectron spectroscopy helped establish the 3-pyridyl thiadiazoles mode of action toward corrosion. Adsorption of the 3-pyridyl on the mild steel surface in 1M HCIO4 follows the Langmuir adsorption isotherm model and the surface analysis showed corrosion inhibition by the 3-pyridyl derivative is due to the formation of chemisorbed film on the steel surface. 

The most conventional investigations on the adsorption of both modifier and substrate looked for the effect of pH on the amount of adsorbed tartrate and MAA [200], The combined use of different techniques such as IR, UV, x-ray photoelectron spectroscopy (XPS), electron microscopy (EM), and electron diffraction allowed an in-depth study of adsorbed tartrate in the case of Ni catalysts [101], Using these techniques, the general consensus was that under optimized conditions a corrosive modification of the nickel surface occurs and that the tartrate molecule is chemically bonded to Ni via the two carbonyl groups. There were two suggestions as to the exact nature of the modified catalyst Sachtler [195] proposed adsorbed nickel tartrate as chiral active site, whereas Japanese [101] and Russian [201] groups preferred a direct adsorption of the tartrate on modified sites of the Ni surface. 

Adsorption of e.g. rosin (abietic acid) at the pigment surface may - depending on the concentration of the rosin - reduce or accelerate the crystal growth. The presence of an excess amount of rosin during the production of diarylide yellow pigments of the Pigment Yellow 13 type affords an additional crystal modification, which can be identified by X-ray diffraction spectroscopy [4],... 

Buckley, A. N., 1994. A survey of the application of X-ray photoelectron spectroscopy to flotation research. Colloids Surf, 93 159 - 172 Buckley, A. N. and Woods, R., 1995. Identifying chemisorption in the interaction of thiol collectors with sulphide minerals by XPS adsorption of xanthate on silver and silver sulphide. Colloids and Surfaces A Physicochemical and Engineering Aspects, 104,2 - 3 Buckley, A. N. and Woods, R., 1996. Relaxation of the lead-deficient sulphide surface layer on oxidized galena. Journal of Applied Electrochemistry, 26(9) 899 - 907 Buckley, A. N. and Woods, R., 1997. Chemisorption—the thermodynamically favored process in the interaction of thiol collectors with sulphide minerals. Inert. J. Miner. Process, 51 15-26... 

Costa, M. C., Botelho, do Rego A. M., Abrants, L. M., 2002. Characterization of a natural and an electro-oxidized arsenopyrite a study on electro-chemical and X-ray photoelectron spectroscopy. Inter. J. Miner. Process, 65 83 - 108 Dai Jingping, Sun Wei, Cao Limei, Hu Yuehua, 2000. Influence of mechanical excitation on adsorption of sodium diethyl dithioformate on galena and sphalerite. Trans. Nonferrous Met. Soc., China, 10 101 - 105... 

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