Platinum conversion data

Besser et al. [53] have studied the hydrogenation of cyclohexane over a platinum catalyst. They used microstructured chips with channel widths of 100 pm and 5 pm and showed that the conversion in the smaller channels is larger, as expected, due to a larger surface-volume ratio. The conversion data were consistent with data from macro-scale reactors. 

The fit of these equations to the data is very good, as seen in Fig. 18. These equations are valid to very small values of CO concentrations, where the reaction becomes first order with respect to CO. In a mixture of CO with oxygen, there should be a maximum in reaction rate when the CO concentration is at 0.2%, as shown in Fig. 19. When the oxidation of olefins and aromatics over a platinum loaded monolith is over 99% complete, the conversion of higher paraffins may be around 90% and the conversion of the intractable methane is only 10%. 

Fig. 2. The selectivity of saturated products (2MP + 3MP + MCP) and benzene produced from n-hexane (total conversion = 100%) as a function of the final hydrogen pressure. Thick full lines represent calculated equilibrium concentrations. Dashed lines denote experimental data with respect to benzene (x ) and saturated Cg products (O). Pulse system, catalyst 1.0 g platinum black, T = 327 3°C ( 600 K) (31).

From this beginning, an extensive study of the isomerization of n-heptane was made with platinum on silica-alumina catalysts. Figure 2 shows curves plotted from the data obtained illustrating the total isomer yield versus conversion and the temperatures that produced these conversions. The conversion-isomer yield curve follows closely the 45° theoretical yield line, goes through a maximum at about 65% isomer yield, and then drops sharply because of cracking. The temperature at which the maximum yield of isomers was obtained was about 660° F. 

A study of the kinetics of isomerization of n-pentane at 372°C. over a platinum on alumina catalyst (0.3% platinum) has been reported by Sinfelt et al. (S4). The rate measurements were made in a flow system at low conversion levels (4-18%). The n-pentane was passed over the catalyst in the presence of hydrogen at total pressures ranging from 7.7 to 27.7 atm. and at hydrogen to n-pentane ratios varying from 1.4 to 18. Over this range of conditions the rate was found to be independent of total pressure and to increase with increasing n-pentane to hydrogen ratio (Fig. 4). The rate data were correlated by an expression of the form... 

It is interesting also to compare the results of the present experiment, which shows directly that a competitive mechanism occurs in the co-adsorption of NO and CO, with previous studies on several surfaces of the platinum group metals. On Pt(lll) and Pt(110), Lambert and Comrie (65) have inferred from thermal desorption data that gaseous CO displaces molecular NO from the surface and causes also a conversion between two thermal desorption states of molecular NO. Similarly, Campbell and White (55) report that adsorbed CO inhibits the oxidation of CO by NO at low temperature on polycrystalline Rh. They attribute this to the occupation of sites by CO which are required for NO adsorption and dissociation. Conrad et al. (66) have used UV-photoelectron spectroscopy to observe directly the displacement of molecular NO by gaseous CO from Pd(110) and polycrystalline Pd surfaces. Thus, it appears that adsorption of molecular CO and NO is competitive on these... 

A convenient method to produce porous surfaces is the anodic oxidation of aluminum plates. Such microstructured aluminum platelets have been coated by wet impregnation with Pt-, V- and Zr-precursors [35], and tested under catalytic methane combustion conditions. The conversion rate of oxygen followed directly the platinum content in the catalysts. These data were well reproducible even after five different runs. 

Figure 3.52 Conversion and selectivity data for the hydrogenation of cyclohexane on a platinum catalyst in micro structured channels with widths of 100 and 5 pm [133]...

Because Pd-based metal membranes, commonly used for hydrogen separation [11] are not resistant towards sulphur, not much research has been performed on the use of such membranes in H2S dehydrogenation reactors. Some success has, however, been reported by Edlund and Pledger [12], They developed a platinum-based layered metal membrane that could resist irreversible attack by H2S at 700°C. At this temperature a conversion of 99.4% was achieved in the membrane reactor. Without hydrogen removal the conversion was only 13%. No permeance data is provided, but platinum-based metal membranes are known for their low hydrogen permeance [14], Johnson-Matthey developed palladium composite membranes with a hydrogen permeance of about 1 10 mol/m sPa [14], but these are most probably not resis-... 

Hindin et al. (18) published data showing benzene formation to proceed readily from methylcyclopentane over mechanical mixtures of platinum bearing particles and silica-alumina, at atmospheric pressure and near 500°C. temperature. Under these conditions the equilibrium constant for conversion of a cyclopentane to a cyclopentene is of the order of unity. Consequently, the first step, if it is catalyzed by X, can itself proceed with... 

Some experimental data obtained by Smith et al. (18) will be used to illustrate the method of approach. These data were obtained with a pressurized all glass flow reactor at a temperature of 399°. The catalyst used was 0.05% platinum on -alumina prepared by impregnating the alumina with chloroplatinic acid. The chlorine introduced by this method of impregnation was removed to reduce the acidity of the catalyst so that the isomerization of cyclohexene to methyl cyclopentane was suppressed. The amount of conversion was varied by changing the amount of catalyst in the reactor. The catalyst bed in the reactor consisted of 15 ml of crushed vycor (60-100 mesh) in which the desired amount of finely crushed (100-200... 

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