Redox reactions hydrogenolysis

The objective of this work was to compare the catalytic properties of Pt-Re/Al203-Cl catalysts prepared either by the surface redox reaction or by classical coimpregnation. According to Augustine and Sachtler [15-16], the interactions between platinum and rhenium were probed by using hydrogenolysis of cyclopentane as a test reaction. 

In the field of organic chemistry, the main applications using bimetallic catalysts prepared by surface redox reactions were for selective hydrogenation and hydrogenolysis reactions. 

When iron is added as a second promoter, the performance of PtFeWZ catalysts is dramatically improved in the presence of dihydrogen in the feed.19,21 Under identical reaction conditions, PtFeWZ(S) is characterized by an n-pentane isomerization rate of 9 x 10 x mol s 1 m 2. Whereas the PtWZ catalyst is characterized by a nearly stable selectivity of about 95% (see Table 2), the PtFeWZ(S) catalyst develops a selectivity (increasing with TOS) of up to 98%, and PtFeWZ(N) shows a stable selectivity greater than 99%. The suppression of the hydrogenolysis products, which are formed on the platinum in PtWZ by the addition of iron as a second promoter, might be a consequence of the suppression of the formation of metallic platinum. Furthermore, the redox properties of the Fe3+/Fe2+ pair in the surface solid solution (see above) might... 

Obviously a controlled preparation of bimetallic catalysts is needed in order to imderstand its role upon activity, selectivity and deactivation resistance. On this way, the controlled formation of surface bimetallic particles has been reported in catalysts prepared by the redox method [1]. In the present work, in order to define the role of the redox method in the surface properties of the R-Au alumina supported catalysts, we report the preparation, characterization and catalytic properties of a set of bimetallic catalysts with different gold content. The catalysts were evaluated using methylcyclopentane (MCP) hydrogenolysis as the test reaction. 

The fluoro derivatives of 1,6-anhydrohexopyranoses undergo all of the common reactions of 1,6-anhydrohexoses. By using a redox sequence, derivatives of l,6-aiihydro-/3-D-allopyranose were prepared545 from 183 and 185. Ammonolysis of the fluoro epoxide 184 leads to the amino derivative381 190, and hydrogenolysis of 184 gives... 

Nevertheless, there are no great differences in the product distribution occur after an oxidation-reduction cycle. On both catalysts the selectivity in isomers is increased after an oxidative reaction. The values of the ratio 3-MP/n-H obtained from the methylcyclopentane hydrogenolysis are not modified by this redox cycle. 

REDOX BEHAVIOR OF ENVIRONMENTAL CONTAMINANTS 269 This approach can be illustrated using the following hydrogenolysis half-reaction CHCI3 -b H+ -b 2e CH2CI2 -b Cr... 

Transition-metal-silyl complexes are also formed by the reactions of metal-alkyl complexes with silanes to form free alkane and a metal-silyl complex. Two examples are shown in Equations 4.114 and 4.115. ° The synthesis of silyl complexes by this method has been accomplished with both early and late transition metal complexes. The formation of metal-silyl complexes from late-metal-alkyl complexes resembles the hydrogenolysis of metal-alkyl complexes to form metal hydrides and an alkane. The mechanisms of these reactions are discussed in Chapter 6. In brief, these reactions with late transition metal complexes to form silyl complexes typically occur by a sequence of oxidative addition of the silane, followed by reductive elimination of alkane. An example of this is shown in the coupling of 1,2-bis-dimethylsilyl benzene with a dimethyl platinum(II) complex (Equation 4.114). Similar reactions occur with d° early metal complexes by a a-bond metathesis process that avoids these redox events. For example, the reaction of Cp ScPh with MesSiH, has been shown to proceed through this pathway (Equation 4.115). ... 

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