Platinum on alumina catalyst

They represent an improvement over earlier platinum on alumina catalysts in their abiHty to resist coke fouling when operated at low pressures. Dehydrogenation and hydrogenation occur on the active metal sites isomerization takes place on the acidic alumina surface. 

Standard Test Methodfor Surface Area of Catalysts. (D3663—78) Standard Test Method for Hydrogen Chemisorption on Supported Platinum on Alumina Catalysts. (D3908-80) American Society for Testing and Materials (ASTM), Philadelphia, PA. 

Aryl or vinyljluoroformates, when passed in the vapor phase with helium over an alumina or platinum on alumina catalyst eliminate carbon dioxide to give, respect vely,/ZMOroare er or vinyl fluorides [id] (equation 26)... 

Barnett et al. [AIChE J., 7 (211), 1961] have studied the catalytic dehydrogenation of cyclohexane to benzene over a platinum-on-alumina catalyst. A 4 to 1 mole ratio of hydrogen to cyclohexane was used to minimize carbon formation on the catalyst. Studies were made in an isothermal, continuous flow reactor. The results of one run on 0.32 cm diameter catalyst pellets are given below. 

Davis (94b) aromatized several Cg and C9 hydrocarbons with a quaternary carbon atom over chromia- and platinum-on-alumina catalysts. Here the reactions of 1,1-dimethylcyclohexane, and 2,2- and 3,3-dimethylhexanes will be compared (Table V). 1,1-Dimethylhexane suffered demethylation predominantly over chromia and alkaline platinum however, with less alkaline platinum, isomerization to xylenes occurred. 

In Figure 5 the conversion of 1-phenylethanol and the open circuit potential of alumina-supported catalysts are plotted as a function of reaction time. There is a striking difference between the curves of unpromoted (a, a ) and bismuth-promoted (c, c ) catalysts. When air is introduced to the reactor, the potential of the platinum-on-alumina catalyst quickly increases to the anodic direction and after one minute the catalyst potential is above -300 mV. One may conclude that there is practically no hydrogen on the platinum surface and after a short period an increasing fraction of platinum is covered by OH. The influence of bismuth promotion is a higher reaction rate (final conversion) and lower catalyst potential during reaction. 

One of the most extensively used addition reactions of cyclobutanes is hydrogenolysis.36 With regard to the mechanistic aspect, evidence has been provided that hydrogenolysis of cyclobutane is structure sensitive to the particle size of the platinum on alumina catalysts.37 Moreover, a kinetic study has also revealed that the mechanism for the hydrogenolysis of cyclobutanes is likely to be different from that for cyclopropanes.37... 

The foregoing paragraphs have described platinum on alumina catalysts in a very general way and have also attempted to give a brief discussion of the reason why platinum is so commonly used as a reforming catalyst. In the following sections, the physical and chemical properties of platinum-alumina catalysts will be discussed in more detail, since this information will be of considerable help in understanding the way in which these catalysts function. 

McHenry and co-workers (Ml) have suggested that platinum on alumina catalysts, which are active for the dehydrocyclization of paraffins,... 

Sinfelt and associates (S6) for a 0.3% platinum on alumina catalyst. At these temperatures diffusional effects are much less important than at the usual reforming temperatures. Over the range of methylcyclohexane and hydrogen partial pressures investigated, 0.07 to 2.2 atm. and 1.1 to 4.1 atm., respectively, the reaction was found to be zero order with respect to hydrogen and nearly zero order with respect to methylcyclohexane (Table III). The kinetic data were found to obey a rate law of the form... 

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... 

Addition. Vinyl chloride undergoes a wide variety of addition reactions. Chlorine adds to vinyl chloride to form 1,1.2-tnchloroethane by either an ionic or a radical path. Hydrogen halides add to vinyl chloride, usually to yield the 1.1-adduct. Many other vinyl chlonde adducts can be formed under acid-catalyzed Fnedel-Crafts conditions. Vinyl chloride can be hydrogenated to ethyl chloride and ethane over a platinum on alumina catalyst. 

The results of Shephard and Rooney support these observations. The activation energy for n-propylbenzene over platinum-on-alumina catalyst is twice that of the cyclization of 1-methyl-2-ethylbenzene (11.6 versus 5.8 kcal/mol Fig. 2). However, these last values are based on pulse-reactor results therefore, they should be used only for qualitative comparisons. 

This reaction was first observed by Plate, Erivanskaya, and Khalima-Mansur over platinum-on-carbon and platinum-on-alumina catalysts (43-48). Platinum-on-carbon catalyzes this reaction between 310°C and 390°C (above which the catalyst is poisoned) (44). Over an acidic platinum-alumina catalyst containing 0.5 wt% platinum and 0.1 wt% sodium, 16.7% acenaphthenes and 1.5% acenaphthylene are obtained at 460°C and at 0.4 liquid hourly space velocity in hydrogen diluent. Conversions are considerably lower in helium. 

In some cases a catalyst consists of minute particles of an active material dispersed over a less active substance called a support. The active material is frequently a pure metal or metal alloy. Such catalysts are called supported catalysts, as distinguished from unsupported catalysts, whose active ingredients are major amounts of other substances called promoters, which increase the activity. Examples of supported catalysts are the automobile-muffler catalysts mentioned above, the platinum-on-alumina catalyst used in petroleum reforming, and the vanadium pentoxide on silica used to oxidize sulfur dioxide in manufacturing sulfuric acid. On the other hand, the platinum gauze for ammonia oxidation, the promoted iron for ammonia synthesis, and the silica-alumina dehydrogenation catalyst used in butadiene manufacture typify unsupported catalysts. 

Smith et al. (18) have studied the reaction cyclohexane benzene - - 3Ha over platinum on alumina catalyst. The methods of this article were used to test whether the reaction scheme... 

Similar results have been reported for platinum on alumina catalysts. See den Otter, G. J. Dautzenberg, F. M. J. Catal. 1978, 53, 116-125. 

Fio. 10. First-order plot of the hydrogenation of 1-methylnaphthalene ( ) and 2-methylnaphthalene (O) at 1000 psig hydrogen pressure and 200° over a 0.6% platinum-on-alumina catalyst. 

Example 9-2 Olson and Schuler determined reaction rates for the oxidation of sulfur dioxide, using a packed bed of platinum-on-alumina catalyst pellets. A differential reactor was employed, and the partial pressures as measured from bulk-stream compositions were corrected to fluid-phase values at the catalyst surface by the methods described in Chap. 10 (see Example 10-1). The total pressure was about 790 mm Hg. 

The reaction + 5O2 - H2O occurs with a platinum-on-alumina catalyst at low temperatures. Following the work of Maymo and Smith, suppose that the rate, in g moles 02/(sec)(g catalyst), at the catalyst surface is given by... 

The studies of n-heptane and methylcyclopentane conversion provide insight into the advantages of platinum-iridium and platinum-rhenium catalysts over catalysts containing only one of the transition metal components, that is, platinum, iridium, or rhenium. If, for example, we consider an iridium-alumina catalyst for the reforming of a petroleum naphtha fraction, we find that it produces a substantially higher octane number reformate than a platinum on alumina catalyst under normal reforming conditions. The iridium-alumina catalyst will also exhibit a lower rate of formation of carbonaceous residues on the surface, with the result that the maintenance of activity with time will be much superior to that of a platinum-alumina catalyst. 

B) The product from A is then fed to an isomerization unit containing, in this example, a fluoride platinum-on-alumina catalyst, which... 

Rowan [45] investigated the applicability of hydrogenation and dehydrogenation reactions in gas chromatography for analytical purposes. He showed that it is not a complicated problem to carry out selective hydrogenation of aromatic hydrocarbons and olefins as a group reaction. It was shown that a 1.4% platinum on alumina catalyst... 

The overall activation energies and frequency factors of overall catalytic rate expressions, and consequently their temperature coefficients, are less easy to constrain. For example, the relatively simple rate expression for the DAM model of the oxidation of carbon monoxide on a platinum on alumina catalyst (see Chapter 11) is thought to be ... 

An alternative method for oxygen removal is catalytic reduction over a platinum-on-alumina catalyst in the presence of methanol [22,23]. A short column packed with the catalyst is inserted between the pump and injector. Provided that the mobile phase contains about 1% methanol (or more) oxygen is very efficiently reduced producing formaldehyde and formic acid. It is necessary to ensure that these products do not react with or degrade the sample. An in-line chelation column placed between the pump and injection valve was suitable for the removal of metal impurities from the mobile phase [24]. 

Sinfelt, Hurwitz, and Rohrer [J.H. Sinfelt, H. Hurwitz and J.C. Rohrer, J. Phys. Chem., 64,892 (I960)] studied the kinetics of the isomerization of n-pentate over a platinum-on-alumina catalyst in the presence of excess hydrogen. Overall,... 

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