Catalysts, general hydrogen reduced

The available surface area of the catalyst gready affects the rate of a hydrogenation reaction. The surface area is dependent on both the amount of catalyst used and the surface characteristics of the catalyst. Generally, a large surface area is desired to minimize the amount of catalyst needed. This can be accomphshed by using either a catalyst with a small particle size or one with a porous surface. Catalysts with a small particle size, however, can be difficult to recover from the material being reduced. Therefore, larger particle size catalyst with a porous surface is often preferred. A common example of such a catalyst is Raney nickel. 

The enhanced activity of transition metal catalysts supported on reducible oxides in the selective hydrogenation of the C=0 bond is generally attributed to... 

In most catalytic hydrogenation reactions of the keto functional group by rhodium and iridium complexes, Hj is cleaved homolytically by the metal which then assists the reductive elimination of the alcohol. In contrast, ruthenium catalysts generally reduce ketones to alcohols with ionic mechanisms involving the heterolytic splitting of H2 [60] (Scheme 12). Obviously this is only a general... 

Hydrogenation of carbon-carbon double bonds takes place easily and in most cases can be effected under mild conditions. Only a few highly hindered alkenes are resistant to hydrogenation, and even these can generally be reduced under more vigorous conditions. Palladium and platinum are the most-frequently used catalysts. Both are very active and the preference is determined by the nature of other functional groups in the molecule and by the degree of selectivity required (platinum usually... 

Dehydrogenation—In general, hydrogenation catalysts can also remove hydrogen from organic compounds. The production of olefins and diolefins fiom paraffins is an important commercial process. Formation of butene from butane is favored at about atmospheric pressures while butadiene is favored at reduced pressures. 

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