# What is difference between hydrogenation and hydrogenolysis?

Hydrogenation refers to the reaction between a susbtance and molecular hydrogen ${H}_{2}$. The substance could be, for example, an organic compound such as an olefin, which is being saturated (ethylene --> ethane), or could be substance undergoing reduction. The process usually takes place in the presence of a calalyst (e.g. palladium on graphite).