Platinum, coadsorption

Lin W-F, Sun S-G, Tian Z-W. 1994. Investigations of coadsorption of carbon monoxide with S or Bi adatoms at a platinum electrode by in-situ FTIR spectrocopy and quantum chemistry analysis. J Electroanal Chem 364 1-7. 

Here, the dissociative adsorption of hydroi l radicals increases with increasing coadsorption of electropositive potassium atoms on the platinum surface. It has also been reported that coadsorption of electronegative oxygen molecules accelerates the adsorption of hydroxjd radicals on the surface of copper, silver and nickel [Thiel-Madey, 1987]. 

It was demonstrated that the radiotracer method, using labeled anions, is an adequate tool to follow anion adsorption in the course of voltammetric measurements and to gain simultaneous information on hydrogen and anion adsorption [163]. Coupling voltammetric and radiometric measurements in the study of platinized platinum electrodes gave insight in the anion-hydrogen atom coadsorption process. 

Fewer nonsteady-state measurements have been carried out on iridium than on platinum and palladium. Figure 50 shows the results of a 02—CO coadsorption experiment on Ir(lll) (203). Initially 02 was adsorbed, followed by CO adsorption, after which the crystal was heated with a linear temperature rise. It is seen that the peak temperature for COz desorption is shifted to lower values with increasing CO coverage. This may be due to a second-order desorption effect (203) or a reduced activation energy for the reaction owing to interactions in the adlayer, as was found on Pd(lll) (176). 

Fig. 1 shows clearly that only one hydrogen consumption peak was found for the bimetallic precursor prepared by coadsorption, which has been assigned to hydrogen conjointly consumed during the reduction of both metals due to the formation of a kind of alloy between platinum and ruthenium. The bimetallic clusters thus formed will be richer in platinum for the CAD series than for the CAC series, due to the metal contents shown in Table 1. 

C and n-octadecane-1,2-H at a concentration of 0.35 molar in stearic acid and studied the coadsorption of stearic acid and octadecane on polished surfaces of silver, platinum, copper and iron. The films were prepared by retraction from the melt at 40 C (at room temperature the mixture was solid). The proportion of n-octadecane in the film was assayed by differential extraction with cyclohexane. The results of the investigation adequately demonstrate that n-octadecane coadsorbs with stearic acid but not necessarily as a mixed oriented monolayer. Some of the data indicate that more than a single layer is present on the surface. Thus the structure of the long-chain material on the surface may be open to conjecture, but that each constituent adsorbs and in what relative amount is directly determined by radioactive assay. 

Another reaction model involves the compression of the ethylidyne overlayer at high pressure of ethylene. Because of repulsive adsorbate-adsorbate (ethylene-ethy-lidyne) interaction, and the expected small activation energy of ethylidyne surface diffusion, ethylene could adsorb on the metal in the small hole created near the compressed ethylidyne. Compression of this type has been detected by STM upon the adsorption of hydrocarbons on platinum and the coadsorption of CO and sulfur on both platinum and rhenium surfaces [218]. 

Radioisotopic tracer techniques were applied to study the coadsorption of n-octadecane and stearic acid on a metal surface immersed in a n-octadecane solution of stearic acid. Dual labeling was employed for determining the surface concentrations of both n-octadecane and stearic acid. n-Octadecane was labeled with tritium and stearic acid with carbon-14. The results of half-hour adsorption experiments provide direct proof of coadsorption of polar and nonpolar materials on iron, copper, silver, and platinum surfaces. The films produced on silver and copper by 19-hour adsorption consisted of approximately one molecular layer of stearic acid and two molecular layers of octadecane. A new model is proposed to describe the structure of this thick coadsorbed film. 

The spectra show two resonances located around 2065 cm and 1965 cm . The first corresponds to linearly bound CO, the latter was assigned to CO in a bridge-bound position [786]. The conversion of CO in a bridging location into species atop has been identified with SFG [794]. The combination of the high light intensity (e.g. free-electron lasers) and the possibility to obtain absolute spectra without any modulation technique has allowed the detection of generally weak bands like those of over- and underpotential deposited hydrogen on a platinum electrode [795, 796]. Studies of coadsorption of cyanide anions and cetylpyridinium cations on Au(l 11) and Au(210) revealed marked differences [797]. CN is bound... 

A challenging problem is to address the effect of adsorbed hydrogen on NMR response of small platinum particles (see Section 3.1.3.2 in Ref 27). EQCM probably presents a separate possibility to get microscopic information if applied less straightforwardly (not reduced to a weighting instrument). This technique is sensitive to hydrogen adsorption and able to tell the difference of sulfate and perchlorate coadsorption with hydrogen (see Ref 238 for a brief review of earUer works). Recently developed EQCM... 

Rodriguez, J.L., Pastor, E. Consecutive adsorption as studied by electrochemical mass spectrometry Coadsorption, desorption and displacement reactions on platinum. Electrochim. Acta 1998, 44, 1173-1179. 

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