Adsorption coadsorption

Synergistic adsorption — Coadsorption of two or more components under conditions (e.g., at concentrations) where neither of them adsorbs alone. 

Thus, the adsorption of methane onto nanosilica A-300, composed of nonporous primary nanoparticles (average diameter 8.1 nm), at standard pressure is a function of temperature and silica hydration. The silica hydration dependence is nonlinear, and maximal adsorption of methane (1.9-1.2 wt% at 200-280 K) is observed at hydration h = 0.l g/g for intact silica. Decrease (on heating) and increase (on wetting) of the silica hydration both lead to a reduction of methane adsorption. Coadsorption of methane and water leads to the appearance of a H NMR signal from WAW at 8h 1 ppm. The amount of this water correlates to concentration of adsorbed methane, because weakly associated bound water is most clustered at the surface of nanosilica composed of nonporous primary nanoparticles. The adsorption of methane on nano/mesoporous... 

Coadsorption Effects on Overall Graft Copolymer Adsorption. Coadsorption effects were explored by varying the sequence of polymer types exposed to the surface, as well as by mixing the polymer types, and then observing the dependence... 

A new spectroscopic method that appears to be promising for answering some basic questions regarding surfactant adsorption, coadsorption, and displacement reactions on charged model surfaces is Surface-Enhanced Raman Scattering (SERS) spectroscopy [1—6]. This enables researchers to characterize in situ the chemical identity, structure, orientation, and chemical reaction of species adsorbed at surfaces. 

Diehl R D and McGrath R 1996 Structural studies of alkali metal adsorption and coadsorption on metal surfaces Surf. Sc/. Rep. 23 43... 

Lateral interactions between the adsorbed molecules can affect dramatically the strength of surface sites. Coadsorption of weak acids with basic test molecules reveal the effect of induced Bronsted acidity, when in the presence of SO, or NO, protonation of such bases as NH, pyridine or 2,6-dimethylpyridine occurs on silanol groups that never manifest any Bronsted acidity. This suggests explanation of promotive action of gaseous acids in the reactions catalyzed by Bronsted sites. Just the same, presence of adsorbed bases leads to the increase of surface basicity, which can be detected by adsorption of CHF. ... 

Electronegative adatoms cause significant changes in the metal surface electronic stmcture, manifest as changes in the surface work function. In general electronegative additives increase the work function of the metal substrate. Typical examples are shown in Figures 2.9 and 2.10 for the adsorption of Cl and coadsorption of Cl and O on the work function of... 

S. Surnev, and M. Kiskinova, Formation of Patchy Surface Overlayers Alkali Adsorption and Alkali Cabon Monoxide and oxygen coadsorption on Ru(001) and Ru(10l 0 Appl. Phys. 46, 323-329 (1988). 

Temperature programmed reaction spectra depicting the reaction of H2O and OH groups with oxygen on Pd(lOO) are shown in fig. 3. Curve (a) was obtained for H2O adsorption on the clean surface and contains two peaks, the state at 167 K of multilayer H2O, and the <>2 state at 182 K due to H2O bound directly to the surface /7/. An additional state at 255 K, labelled y, is observed following coadsorption of 1 0 and 0 (fig. 3b). This state represents the reaction of OH groups III... 

Coadsorption and Decomposition Reactions. The final area we discuss are cases where there are coadsorbed species present, which may react, and cases where molecular adsorption converts to dissociative (or associative) products. 

Diemant T, Hager T, Hosier HE, Rauscher H, Behm RJ. 2003. Hydrogen adsorption and coadsorption with CO on well-defined himetallic PtRu surfaces—A model study on the CO tolerance of himetallic PtRu anode catalysts in low temperature polymer electrolyte fuel cells. Surf Sci 541 137. 

Montanari el al., for example, studied a Co—H-MFI sample through FT-IR spectroscopy of in situ adsorption and coadsorption of probe molecules [o-toluonitrile (oTN), CO and NO] and CH4-SCR process tests under IR operando conditions. The oTN adsorption and the oTN and NO coadsorption showed that both Co2+ and Co3+ species are present on the catalyst surface. Co3+ species are located inside the zeolitic channels while Co2+ ions are distributed both at the external and at the internal surfaces. The operando study showed the activity of Co3+ sites in the reaction. The existence of three parallel reactions, CH4-SCR, CH4 total oxidation and NO to NOz oxidation, was also confirmed. Isocyanate species and nitrate-like species appear to be intermediates of CH4-SCR and NO oxidation, respectively. A mechanism for CH4-SCR has been proposed. On the contrary, Co2+ substitutional sites, very evident and predominant in the catalyst, which are very hardly reducible, seemed not to play a key role in the SCR process [173],... 

Electrochemical reactions are driven by the potential difference at the solid liquid interface, which is established by the electrochemical double layer composed, in a simple case, of water and two types of counter ions. Thus, provided the electrochemical interface is preserved upon emersion and transfer, one always has to deal with a complex coadsorption experiment. In contrast to the solid/vacuum interface, where for instance metal adsorption can be studied by evaporating a metal onto the surface, electrochemical metal deposition is always a coadsorption of metal ions, counter ions, and probably water dipols, which together cause the potential difference at the surface. This complex situation has to be taken into account when interpreting XPS data of emersed electrode surfaces in terms of chemical shifts or binding energies. 

The difference between the potential of the current peak for the desorption and the bulk deposition potential is known as the underpotential shift simple systems the value of Gibbs energies of adsorption and deposition shift both according to the Nernst equation. Deviations from this behavior may indicate coadsorption of other ions. 

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