Platinum computer simulations

H. P. Kaukonen, R. M. Nieminen. Computer simulations studies of the catalytic oxidation of carbon monoxide on platinum metals. J Chem Phys 97 4380- 386, 1989. 

Data obtained on the electrode-oxygen distances and the reorientation of water in the inner layer are consistent with the results of computer simulations. The relative density profile for oxygen at the water/platinum interface shows two distinct maxima at 2.5 and 5.4 A, respectively. The first maximum corresponds to water directly bound to the surface whereas the less pronounced second maximum can be ascribed to the second layer of water linked through hydrogen bonds to the first layer. 

Nakahara and Nishimura studied the selectivities of copper-chromium oxides, nickel, palladium, rhodium, and ruthenium catalysts in the hydrogenation of phenan-threne, 9,10-dihydrophenanthrene (DHP), and 1,2,3,4-tetrahydrophenanthrene (THP), usually in cyclohexane at 80°C (150°C for copper-chromium oxide) and an initial hydrogen pressure of 11 MPa (5 MPa for platinum metals). The hydrogenations over Os-C, Ir-C, and Pt-C were very slow and not investigated further. The varying compositions of the reaction mixture versus reaction time have been analyzed on the basis of the reaction sequences shown in Scheme 11.20 by means of a computer simulation, assuming the Langmuir-Hinshelwood mechanism.262 The results are summarized in Table 11.23. 

In order to test the (in)correctness of the Marcus solvent model, we have carried out extensive MD simulations of a bond-breaking electron-transfer reaction in water at a platinum electrode. Figure 10a shows the computer simulated potential energy surface obtained by a two dimensional umbrella sampling technique. Analysis of the results in Figure 10a brings to light two important effects of the solvent the Marcus model does not account for. 

It was proposed that, in the platinum-rich range, large platinum ensembles are present so that a reaction pathway involving di- and tri-adsorbed intermediates is dominant. As ensemble size becomes small, and the number of platinum atoms much restricted, a second mechanism leading to hydrogenolysis predominates. This interpretation was supported by detailed kinetic evidence and by computer simulation of the ensembles proposed. 

I.Y. Chan, R. Csencsits, M.A. O Keefe, and R. Gronsky, Computer-Simulated Images of Platinum Clusters in the Channels of Y Zeolites Zone-Axis Results. J. Catal., 1987, 103, 466-473. 

The oscillations observed with but-l-ene at 150°C are made up of two different portions. One is of sinusoidal type and the other consists of relaxation jumps between low and high conversion states. The parameters, k and A 4, adsorption and desorption rate constants of but-l-ene on the platinum surface, ks the surface reaction rate constant between O2 and but-l-ene, Zq the capacity factor, change the characteristics of these oscillations. Operating conditions like reactor temperature, flow rate, volume, mass of catalyst and concentration of but-l-ene in the feed also affect these oscillations both experimentally and in computer simulations. 

E. Spohr, J. Phys. Chem., 93, 6171 (1989). Computer Simulations of the Water/Platinum... 

V. Pokhmurskii, S. Komiy, V. Kopylets Computer Simulation of Binary Platinum-Cobalt Nanoclusters Interaction with Oxygen, "Journal of Cluster Science", 22 (3), 449 58(2011). 

Fig. 63 SEM images of crystal-shaped platinum deposits juxtaposed to computer simulations. The dashed red frame marks the area of interest...

Figure 6.3 shows crystal-shaped platinum deposits juxtaposed to the computer simulations. Note that the computer simulation were calculated for a minority phase volume fraction of 12%, while depending on the assumed polymer densities, the copolymer PLA volume fraction lies between 36 and 39 %. As discussed previously, for these high volume fractions the computer model predicts that the < 110> directions form vertices and tlius, increase the number of faces surrounding the < 100 > vertices by a factor of two to a total of 8 facets. 

X. Xia and M. L. Berkowitz, Electric-field-induced restructuring of water at a platinum water interface—a molecular-dynamics computer-simulation, Phys. Rev. Lett, 74, 3193-3196 [1995]. 

We mentioned in the beginning of this chapter that even the most refined experimental studies may not reveal the desired dynamical information if reactants and products become completely thermalized on the surface. This is a serious problem, but there are indications that many situations exist for which detailed dynamical information can be extracted. For one thing, the statement above is not quite correct. Even if everything does thermalize on the surface, important information about interaction potentials might be revealed. An example is provided by the computer simulations of thermal desorption of rare gases from platinum described above. Even though the rare gas atoms have completely equilibrated prior to desorption, distinctive angular and velocity distributions are produced. These... 

Now, theoretical calculation methods of sufficient accuracy may fill the lack of quantitative information concerning so elusive species. On the other hand, the use of a monocoordinated complex as being the simplest molecular model to simulate a chemisorption phenomenon on a metallic surface, for instance the chimisorption of carbon monoxide on iron or nickel [16,17,18] enables to predict the shifts of the CO stretching vibration of the adsorbed species. Similar effects observed with cyanide anions CN on a cathode of platinum, silver or gold, using non-linear optics techniques can be rationalized by computing the CN vibration mode of the corresponding triatomic systems [19,20,21]. 

Figure 1 schematically represents an oxidizer-absorption tower used in nitric acid production. In this tower the nitric oxides generated by high-temperature air oxidation of ammonia on platinum gauze are oxidized and absorbed to yield nitric acid. Koukolik and Marek [49] simulated the behavior of the tower on a digital computer. The following reaction scheme was used ... 

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