Hydrogen adds to alkenes in the presence of metal catalysts
Heterogeneous catalysts: finely divided insoluble platinum, palladium or nickel catalysts
Homogeneous catalysts: catalyst(typically rhodium or ruthenium based) is soluble in the reaction medium
Wilkinson’s catalyst is Rh[(C6H5)3P]3Cl
This process is called a reduction or hydrogenation
An unsaturated compound becomes a saturated (with hydrogen) compound