Heterogenised Catalysts

A study of unsaturated ester hydrogenation by homogeneous and heterogeneous palladium catalysts reveals enhanced selectivity in serbate reduction catalysted by Pd(acac)2 compared with Pd/C . 

Polystyrylbipyridine supported Pd(acetate[2 catalyses the hydrogenation of mono alkenes at atmospheric pressure with selectivity determined by steric hindrance at the double bond and rate decreasing hex-l-ene oct-l-ene cyclohexene cyclooctene . 

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Whatever the configuration and the nature of the process, all of the catalysts examined show high activities and selectivities of up to 90%, but low enantioselectivity (in the best case 64% ee data reported in Table 3). Heterogenised catalysts (entries 2 and 4, Table 3) are slightly better in terms of both... 

Heterogeneous or heterogenised catalysts (Appendix 2) are extensively used in the form of solid oxides for large industrial production (as shown in Section 5.2), but so far have not found significant uses in fine chemicals manufacture, although some attractive routes have been worked out. For... 

In the catalysed hydrosilylation of styrene Avith the selected silanes the influence of the temperature (25°, 38° and 50°C) on turnover, chemical yield and selectivity is summarized in Table 1. All catalysts, homogeneous and heterogenised and silanes show high catalytic activities which increase when increasing of the temperature. This effect is more important on the heterogenised catalysts probably by the effect of the adsorption of reagents into mesopores, which became less decisive at higher temperatures. 

The results of the hydrosilylation reactions carried out without solvent and in a solution of benzene, indicate that the use of a solvent decrease markedly the turnover rates for homogeneous catalysts, however the reactivity order for different silanes and selectivities founded are not sensibly modified. Thus, for more cile and precise comparison between homogeneous and heterogenised catalysts, in where the reaction without solvent was more difficult to standardise, we have employed 1ml of benzene as solvent in the following reactions. 

Table 3. Analytical data of homogeneous and zeolite-heterogenised catalysts...

There have been many successful attempts to include organometallic complexes into zeolites, for example for use as heterogenised catalysts. An interesting variation on this approach is the inclusion of organometallic complexes such as... 

The heterogenised catalysts could be conveniently recovered together after an acidic treatment, reused for up to ten runs maintaining the level of enantioselectiviiy, although with a slight decrease in diol peld. 

Titanium-alkoxide/Aryloxide and Related Heterogenised Catalysts... 

Israelsohn 0., Vollhardt K.P.C., Blum J. Further studies on hydration of alkynes by the PtCU-CO catalyst. J. Mol. Catal. A Chem. 2002 184 1-10 Jamis J., Anderson J.R., Dickson R.S., Campi E.M., Jackson WR. Modified silica-heterogenised catalysts for use in aqueous enantioselective hydrogenations. J. Organomet. Chem. 2001 627 37 3... 

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