Surface adsorbed spedes

Nevertheless, the effect of washing time was also examined. The results were that when the electrode was washed by 60 ml of electrolyte, the shoulder at 700 mV and the broad peak above 1200 mV still existed but their heists were decreased. Therefore they were likely to be attributed to physically adsorbed spedes, possibly methanol itself on the surface of platinum or the glass tube. 

It is oonduded that coke in the initial pnase is formed on the surface through strong adsorption of PNAs. Up to 4% by wei t of the adsorbed spedes (coke) does not significantly affect the HDS activity of the catalyst... 

For all the samples measured, the C13 peak from surface COf ions appears beside the peak of the contamination carbon at 286.4 eV. From Table 2, one can find that for all the samples, the contents of the surface CO are almost similar however, both the amounts of the lattice oxygen and the coordinatively tmsaturated oxygen sharply change from sample to sample. This fact might give a due that the coordinatively unsaturated oxygen spedes cannot be attributed to COf, but to surface adsorbed oxygen. 

P. Hollins, The influence of surface defects on the infrared spectra of adsorbed spedes. Surf Sci. Rep. 16, 51-94 (1992)... 

Adsorption impedance Z may be represented by a parallel combination of resistance R and CPE p, which represents pseudocapadtance created by charge accumulation at the electrode surface. The adsorbed spedes become involved in complex surface-mediated kinetics, such as temperature-driven complexation of the surface-active oil additives [7]. The experimental and modeled data confirmed the presence of two facile adsorption-driven processes—adsorption of at least two different groups of surface-active oil additives (likely to be detergents and antwear agents), and their mutual complexation. 

CH00CH3)t carbon dioxide (C02>. formic acid (HCOOH), and formaldehyde (HCHO) are detected in the solution during the oxidation of methanol on platinum in sulfiiric add. While these are stable and detached spedes, spedes that are unstable or adsorbed on the electrode surface are also expected to be formed. 

In Section 6.4.2 we will find that T represents the Gibbs-surface excess, i.e., T=N/A -N°/A, where is the number of molecules that would have been there if there had been no double layer, and N is the actual number of molecules in the interfacial region. However, when the bulk concentration of the spedes is small, i.e., tfi — 0, then the number of adsorbed molecules tends to f, i.e., f — N/A. 

The perchlorate ions have been found to interact with the Ti02 films (but not with the unreduced anatase powder), forming relatively small amounts of chloride species (cf. Table 1). It seems probable that the latter spedes, arising from the reductive adsorption of the CIO4 ions, were not simply adsorbed but incorporated into the surface region of the Ti02 films, as no irreversible chloride adsorption could be detected from NaCl solutions. 

Methane oxidation at mild or low temperatures can be catalyzed by platinum group metals. Palladium is one of the most efQdent metals (1) and has been studied over mai supports (2-6). This particular metal, when supported on alumina, b ins to show an increase in its activity between 350 and 420°C. At these conditions a general increase in the active spedes particle size is observed. Piimet and Briot (7,8) defined two states for the Pd/Al203 supported catalyst a state I, obtained after simple reduction and a state n after the catalyst had reacted at 600°C for 14 h under 02/CH4=4A. State II was more active than state I and showed a lower binding oietgy of oxygen with palladium. However, the state of the active phase was not clear. The diffoences in activity, also observed by others, have also been related to the formation/decomposition of PdO (9), to the oxygen adsorbed on metallic Pd (2), to the modification of Pd surface spedes (3), and to the reconstruction of PdO crystallites (4, 10). One of the hypotheses for the activation of the Pd catalysts was the establishment of an epitaxy between the metal and the support (8, 11). 

Here, / is the thickness of the adsorbed layer, a " is the induced charge density on the surface of the adsorbed layer which is adjacent to the electrode surface, /, is the permanent dipole moment normal to the electrode surface of the i-th spedes, a is its polarizability, and Eo is the permittivity of vacuum. 

The decreasing amount of NO remaining adsorbed on the catalyst as a function of increasing oxygen coverage is related to saturation of the surface with Pt-NOa and [NOal-AlaOs species and to a limitation of Pt-O-spedes. 

Ousters adsorbed on the outside surfaces of zeolites can often be easily extracted with neutral solvents or with salt solutions which remove the cluster ions by cation metathesis (ion exchange). Comparison of the infrared spectra of the extracted spedes and those of known spedes helps identify the encaged spedes. When treatment of a sample with such solutions fails to remove sorbed dusters, they are inferred to be trapped within the cages. The inference is supported when the same clusters adsorbed on the surface of a large pored material such as an amorphous metal oxide are removed by extraction. 

Cheddie and Munroe presented a one-dimensional model (across the MEA), where the effects of gas solubility are taken into account and a simple submodel for the blocking of catalyst surface sites by adsorbed phosphate spedes is incorporated [22]. The conductivity of the electrolyte and the solubihty of hydrogen and oxygen are taken into account as functions of temperature. The numerical solution shows very good agreement with experimental results. The influence of the phosphoric acid doping level is discussed. One major conclusion of the model is that only 1% of the catalyst surface is utilized in fuel-ceU operation. 

Above the ZPC of titania, the hydroxyls groups of tiiis compound tend to be negatively charged by formation of the deprotonated titania (TiO ) spedes. So that it is relatively difficult for de tungsten ions to be adsorbed on the titania surface, due to the electrostatic repulsions in the solution. Below the ZPC, on the alumina the surface is charged poritively, therefore, tungsten aiuons tend to be adsorbed on die alumina surface. 

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