The site isolation effect by alloys

Here we present two examples of such effects, the dehydrogenation of isobutane into isobutene and the hydrogenolysis of acids or esters into aldehydes and alcohols. Usually the effect of tin, present as a surface alloy, is to dilute the active sites, thus reducing the yield of competitive reactions. 

Selective hydrogenolysis of esters and acids to aldehydes and alcohols 

Hydrogenolysis of esters to aldehydes or alcohols is difficult to achieve either by homogeneous or heterogeneous catalysis. Indeed high temperatures and high pressures are required to achieve the reaction, leading to non-selective hydrogenolysis with formation of acids, alcohols, and hydrocarbons. 

Typically, in the hydrogenolysis of acetic acid, high selectivities towards ethanol ( 87%) are achieved with the Ru-Sn alloy, compared with that of the pure metal, for which the major product is methane. It is also possible to increase the selectivity for the corresponding aldehyde, for example by reducing the ratio of hydrogen to 

This mechanism is comparable to that proposed for the hydrogenolysis of esters. Note also that during the reaction esters are formed which can also undergo the hydrogenolysis reaction, by the mechanism depicted above. 

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