Platinum-Silica catalyst

Fig. 3. Electron micrograph of 2.5% (w/w) platinum/silica catalyst. Prepared by impregnation with chloroplatinic acid, reduced in hydrogen at 210°C. Micrograph obtained by thin sectioning. The black dots are platinum particles. (X 100,000). Reproduced with permission from T. A. Dorling and R. L. Moss, J. Calal. 7, 378 (1967) R. L. Moss, Platinum Metals Rev. 11 (4), 1 (1967), and British Crown Copyright.

Subsequent to the discovery of skeletal rearrangement reactions on plati-num/charcoal catalysts, the reality of platinum-only catalysis for reactions of this sort was reinforced with the observation of the isomerization of C4 and C5 aliphatic hydrocarbons over thick continuous evaporated platinum films (68,108, 24). As we have seen from the discussion of film structure in previous sections, films of this sort offer negligible access of gas to the substrate beneath. Furthermore, these reactions were often carried out under conditions where no glass, other than that covered by platinum film, was heated to reaction temperature that is, there was essentially no surface other than platinum available at reaction temperature. Studies have also been carried out (109, 110) using platinum/silica catalysts in which the silica is catalytically inert, and the reaction is undoubted confined to the platinum surface. 

Platinum is an important example of a metal where, even on an uncontaminated surface such as is offered by an evaporated film, there is a strong tendency for only one C—C bond to be ruptured in any particular reacting molecule. On this basis, one may express the distribution of reaction products in terms of relative C—C bond rupture probabilities. Some data of this sort are contained in Table XI for thick and ultrathin film catalysts, and for comparison there are included some data for reactions on a silica-supported catalyst containing 0.8% platinum. These data all refer to reactions carried out in the presence of a large excess of hydrogen, although the results of Kikuchi et al. (128) indicate that on platinum catalysts the position of C—C bond rupture (in n-pentane) is very little dependent on hydrogen pressure. The data in Table XI show that, on the whole, the 0.8% platinum/silica catalyst used by Matsumoto et al. (110) was inter-... 

Naphthalene see also specific compounds from butylbenzene over platinum-silica catalyst, 23 55... 

With higher hydrocarbons, the spectra depend upon the structure of the olefin [70], With platinum—silica catalysts, linear chain olefins tend to form dehydrogenated surface residues more readily than branched chain olefins, which give predominantly saturated adsorbed alkyl species. 

Triamantane. This diamantoid (2) has been prepared by a multiple rearrangement of (1) in hydrogen in the gas phase on the platinum—silica catalyst. ... 

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