Platinum-silica catalysts hydrogenolysis

The temperature dependence of the selectivity for isomerization versus hydrogenolysis depends on the type of catalyst. Thus, over thick platinum film catalysts this selectivity was temperature independent for the reaction of the butanes and neopentane (24). However, in Boudart and Ptak s (122) reaction of neopentane over platinum/carbon the selectivity to isomerization decreased slightly with increasing temperature while Kikuchi et al. (128) found an increased trend for isomerization in the reaction of n-pentane over platinum/silica and platinum/carbon catalysts. 

Hydrogen and a Catalyst. The most common catalysts are platinum and ruthenium, but homogeneous catalysts have also been used, including copper on silica gel and a ruthenium catalyst on mesoporous silica. Before the discovery of the metal hydrides this was one of the most common ways of effecting this reduction, but it suffers from the fact that C=C, C=C, C=N, and C=N bonds are more susceptible to attack than C=0 bonds. For aromatic aldehydes and ketones, reduction to the hydrocarbon (19-61) is a side reaction, stemming from hydrogenolysis of the alcohol initially produced (19-54). 

Foger and Anderson (739) measured the selectivity and turnover number for isomerization and hydrogenolysis of neopentane on a number of catalysts where platinum was deposited on silica or Y zeolites. The selectivity did not vary widely with metal dispersion down to a limiting value of 10 A, below which isomerization disappears completely. The same trend toward increased selectivity as that observed by Boudart was noted when calcining the catalysts... 

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