Heterogeneous hydrosilation reactions

The range of reactions which have been examined is wide (248) and includes hydrogenations (256), ammonia synthesis (257), polymerizations (257), and oxidations (258). Little activity has occurred in this area during the past few years. Recent reports of the effects of sonication on heterogeneous catalysis include the liquefaction of coal by hydrogenation with Cu/Zn (259), the hydrogenation of olefins by formic acid with Pd on carbon (260), and the hydrosilation of 1-alkenes by Pt on carbon (261). 

The deposition of alkylchains on the hydride surface is performed using heterogeneous phase hydrosilation of terminal unsaturated hydrocarbons (reaction (C)). 

The author s association with industrial hydrosilation processes and research for a number of years has been particularly enlightening in connection with several commercially important reactions and their nuances, oddities and challenges. This has helped the development of certain perspectives on the reaction which will undoubtedly infiltrate parts of this review. It is hoped that these occasional views will enhanee the value of this chapter to the readership. Also, because Ojima s second review was published fairly recently there will be overlap of coverage. However, the organization of this review is not as elaborate and it will only cover hydrosilation occurring, intended to occur or perceived to occur in homogeneous media, except for brief but important comparisons with and discussion on some new developments in the area of heterogeneous catalysis. 

Heterogeneous catalysis is extremely important in the chemical and petroleum industries, and the applications of ultrasound to catalysis have been reviewed recently. The effects of ultrasound on catalysis can occur in three distinct stages (i) during the formation of supported catalysts, (ii) activation of pre-formed catalysts, or (iii) enhancement of catalytic behavior during a catalytic reaction. In the cases of modest rate increases, it appears likely that the cause is increased effective surface area this is especially important in the case of catalysts supported on brittle solids. More impressive accelerations, however, have included hydrogenations and hydrosilations by Ni powder. 

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