Adsorption site, determination

TABLE 4.2. CO Adsorption Sites (Determined by LEED) and C-O Stretch Frequencies... 

The major role of TOF-SARS and SARIS is as surface structure analysis teclmiques which are capable of probing the positions of all elements with an accuracy of <0.1 A. They are sensitive to short-range order, i.e. individual interatomic spacings that are <10 A. They provide a direct measure of the interatomic distances in the first and subsurface layers and a measure of surface periodicity in real space. One of its most important applications is the direct determination of hydrogen adsorption sites by recoiling spectrometry [12, 4T ]. Most other surface structure teclmiques do not detect hydrogen, with the possible exception of He atom scattering and vibrational spectroscopy. 

To determine adsorption sites and thin-film growth modes in a chemically specific manner... 

When the adsorption step determines the rate, component A no longer retards the reaction. Any A that is adsorbed will quickly react, and the concentration of [AS] sites will be low. Note that the desorption step is now treated as being reversible. Thus, any P in the gas phase will retard the reaction even if the surface reaction is irreversible, kr = 0. 

The adsorption of NH3 was also measured with a microcalorimeter, and some of the results are shown in Fig. 3. Figure 4 compares the amount of H2 site determined by the deconvolution analysis with that of super strongly adsorbed NH3 with the heat of adsorption above 155 kJ mol . A good correlation shown in the figure indicates the validity of the amounts of Ga sites determined by the deconvolution analysis. 

The sticking coefficient of H2 on a metal has been determined through an adsorption experiment. The metal surface is assumed to have No = 1.5 x 10 sites m and each adsorption site is assumed to be occupied by one hydrogen atom when the surface is saturated. The experiment was performed by exposing the surface to a known pressure of hydrogen over a well-defined period of time (dosis) and then sequentially determining how much was adsorbed by, for example, TPD. All adsorption experiments where performed at such low temperatures that desorption could be neglected. 

The major addic sites on H-MOR are Bronsted sites determined by pyridine adsorption studies above 80 % of addic sites are Br0nsted sites and the rest are Lewis add sites [4,5]. After adsorption of NH3, 0.3 kPa of EA are admitted on H-EDTA-MOR at 473 K (Figure 6F) adsorbed NH3 is easily replaced by EA to produce deformation bands of NH3+ (1597 cm-i, 1497 cm-t), CH2 (1460 cm-i). This spectrum is quite the same as the spectrum in Figure 6A. The results suggest that adsorption of EA is much stronger than that of NH3. When adsorbed EA is heated up to 573 K (Figure 6G-6H), the spectra are almost the same as the spectra in Figure 6B and 6C. 

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. 

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. 

A COH species requires three adjacent adsorption sites. Under conditions of large degrees of coverage, the site requirement should be an important factor in determining the kind of adsorbate formed. 

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