Surface anion effects

Housmans THM, Koper MTM. 2005b. CO oxidation on stepped Rh[n(lll) x (111)] single-crystal electrodes Anion effects on CO surface mobility. Electrochem Commun 7 581-588. 

Markovic NM, Lucas CA, Rodes A, Stamenkovic V, Ross PN. 2002. Surface electrochemistry of CO on Pt(lll) Anion effects. Surf Sci 499 L149-L158. 

The effect of mixtures of surfactants and polyelectrolytes on spontaneous, water-catalysed hydrolysis (Fadnavis and Engberts, 1982) was mentioned in Section 4, but mixtures of functionalized polyelectrolytes and cationic surfacants are effective deacylating agents (Visser et al., 1983). Polymerized isocyanides were functionalized with an imidazole group and the deacylation of 2,4-dinitrophenyl acetate in the polyelectrolyte was speeded by addition of single or twin chain quaternary ammonium ion surfactants, up to a plateau value. Anionic surfactants had essentially no effect. It is probable that the cationic surfactants accelerate the reaction by increasing the deprotonation of the imidazole groups. 

The influence of antimony at a level of 300 ppm in copper electrolysis is also significant. The morphologies of deposits made from a pure acid-copper sulfate electrolyte and from an identical solution to which the antimony was added are shown in Figures 5 and 6. There are many other combinations of impurities and electrolytes which exhibit this changing surface appearance and deposit orientation besides those selected as examples. Anion effects are also not uncommon, with the halogens often causing the more notable changes. 

On hydrophobic surfaces, similar effects probably occur and can explain the difference in adsorption of an anionic surfactant in the absence and presence of a nonionic surfactant above the CMC on carbon (78) ... 

In dynamic ETEM studies, to determine the nature of the high temperature CS defects formed due to the anion loss of catalysts at the operating temperature, the important g b criteria for analysing dislocation displacement vectors are used as outlined in chapter 2. (HRTEM lattice images under careful conditions may also be used.) They show that the defects are invisible in the = 002 reflection suggesting that b is normal to the dislocation line. Further sample tilting in the ETEM to analyse their habit plane suggests the displacement vector b = di aj2, b/1, 0) and the defects are in the (120) planes (as determined in vacuum studies by Bursill (1969) and in dynamic catalysis smdies by Gai (1981)). In simulations of CS defect contrast, surface relaxation effects and isotropic elasticity theory of dislocations (Friedel 1964) are incorporated (Gai 1981). 

To prevent such anionic effects, so-called anionic sites are conventionally used as additives for ISE membranes. In fact, upon addition of 84, the SHG response of membrane 80 to KSCN was improved (data not shown). This result suggests that the lipophilic anion assists the surface orientation of the 80-K complexes by inhibiting the uptake of SCN" from the adjacent aqueous solution. 

The non-ionic surfactant gives higher adsorbed amounts at the same concentration than the anionic surfactants. This is especially valid at low concentrations, whereas at very high concentrations both surfactants reach the same plateau value. For a hydrophilic solid surface this effect can be just the opposite due to a higher affinity of anionic surfactant to the surface via specific interactions. 

The present article was stimulated by the recent experimental data on protein-covered latex colloidal systems immersed in various electrolyte solutions NaCl, NaNC>3, NaSCN and Ca(NOg)2, which showed strong specific anionic effects on the restabilization curves.1 In the opinion of Lopez-Leon et al.,1 the above polarization model for double layer/hydration forces could explain only some of their experiments, but not all of them. However, they assumed that at pH = 10 the adsorption of anions was negligible hence specific anion effects could not be predicted by their association with the positive sites of the surface. Furthermore, at pH = 4 they assumed the... 

It was recently suggested1 that some of the strong specific anionic effects observed regarding the coagulation of protein-covered latex particles cannot be predicted by a theory of hydration/double layer interaction,5 7 which accounts for the correlation between neighboring dipoles and the formation of dipoles on the surface.10 11... 

Mussini, P.R., Ardizzone, S., Cappelletti, G., Longhi, M., Rondinini, S. and Doubova, L.M. (2003) Surface screening effects by specifically adsorbed halide anions in the electrocatalytic reduction of a model organic halide at mono- and polycrystalline silver in acetonitrile. J. Electroanal. Chem. 552, 213-221. 

Pergolese B, Muniz-Miranda M, Bigotto A (2005) Surface enhanced Raman scattering investigation of the halide anion effect on the adsorption of 1,2,3-triazole on silver and gold colloidal nanoparticles. J Phys Chem B 109 9665-9671... 

The presence of solution can dramatically affect dissociative chemisorption. In the vapor phase, most metal-catalyzed reactions are homolyticlike, whereby the intermediates that form are stabilized by interactions with the surface. Protic solvents, on the other hand, can more effectively stabilize charge-separated states and therefore aid in heterolytic activation routes. Heterolytic paths can lead to the formation of surface anions and cations that migrate into solution. This is directly relevant to methanol oxidation over PtRu in the methanol fuel cell. The metal-catalyzed route in the vapor phase would involve the dissociation of methanol into methoxy or hydroxy methyl and hydrogen surface intermediates. Subsequent dehydrogenation eventually leads to formation of CO and hydrogen. In the presence of an aqueous media, however, methanol will more likely decompose heterolytically into hydroxy methyl (—1) and intermediates. 

Hgure 8 The effect of reactive surface oxygen site density (sites per unit surface anion) on the calculated selectivity at800°C, 0..3 atm CH4,0.03 atm Oj, and 8-ms reaction time. ... 

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