Homogenous platinum catalysts

Silicones. Homogeneous platinum catalysts, used in siUcone manufacture, are retained in the product. This has been shown to impart improved fire resistance in speciali2ed mbbers. 

Pt(0) (vinylMe2Si-0-SiMe2vinyl)i 5 Karstedt s catalyst, platinum divinyltetramthyldisiloxane complex Scheme 1 Homogeneous platinum catalysts... 

Scheme 1. New homogeneous platinum catalysts for the hydrosilylation reaction.

Homogeneous catalysts have been reported, which can oxidize methane to other functionalized products via C-H activation, involving an electrophilic substitution process. The conversion of methane into methyl bisulfate, using a platinum catalyst, in sulfuric acid, has been described. The researchers found that a bipyrimidine-based ligand could both stabilize and solubilize the cationic platinum species under the strong acidic conditions and TONs of >500 were observed (Equation (5)).13... 

In order to evaluate the catalytic characteristics of colloidal platinum, a comparison of the efficiency of Pt nanoparticles in the quasi-homogeneous reaction shown in Equation 3.7, with that of supported colloids of the same charge and of a conventional heterogeneous platinum catalyst was performed. The quasi-homogeneous colloidal system surpassed the conventional catalyst in turnover frequency by a factor of 3 [157], Enantioselectivity of the reaction (Equation 3.7) in the presence of polyvinyl-pyrrolidone as stabilizer has been studied by Bradley et al. [158,159], who observed that the presence of HC1 in as-prepared cinchona alkaloids modified Pt sols had a marked effect on the rate and reproducibility [158], Removal of HC1 by dialysis improved the performance of the catalysts in both rate and reproducibility. These purified colloidal catalysts can serve as reliable... 

Table II summarizes the systems that have been studied as hydrogenation catalysts. The majority of these involve ds metal complexes mainly rhodium(l), palladium(II), and platinum(II), which have been found to be the most successful of the homogeneous hydrogenation catalysts.

Ghaffai, T, and Parkins, A.W. (1995) A new homogeneous platinum containing catalyst for the hydrolysis of nitriles. Tetrahedron Lett., 36, 8657-8660. 

Fig. 20. Dependence of exit conversion on inlet temperature. Platinum catalyst diluted with inert particles (homogeneous mixing) linear velocity w = 5.3 cm, bed length L = 6 cm.

If a chemical reaction is operated in a flow reactor under fixed external conditions (temperature, partial pressures, flow rate etc.), usually also a steady-state (i.e., time-independent) rate of reaction will result. Quite frequently, however, a different response may result The rate varies more or less periodically with time. Oscillatory kinetics have been reported for quite different types of reactions, such as with the famous Belousov-Zha-botinsky reaction in homogeneous solutions (/) or with a series of electrochemical reactions (2). In heterogeneous catalysis, phenomena of this type were observed for the first time about 20 years ago by Wicke and coworkers (3, 4) with the oxidation of carbon monoxide at supported platinum catalysts, and have since then been investigated quite extensively with various reactions and catalysts (5-7). Parallel to these experimental studies, a number of mathematical models were also developed these were intended to describe the kinetics of the underlying elementary processes and their solutions revealed indeed quite often oscillatory behavior. In view of the fact that these models usually consist of a set of coupled nonlinear differential equations, this result is, however, by no means surprising, as will become evident later, and in particular it cannot be considered as a proof for the assumed underlying reaction mechanism. 

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