Hydrogenation of alkyne-alkene mixtures of small sized hydrocarbons has been traditionally performed with Pd-based catalysts modified by a second metal. Over the last few years, this hydrogenation process has become a thriving field to understand selective processes that might be applicable to more complex molecules, for instance those derived from biomass. We summarize here the large body of experimental and open industrial documents to show the properties of different catalytic formulations, we concentrated on the role of the secondary metals employed. We compare these results to theoretical work performed over the last few years and to our new results based on Density Functional Theory. With this insight, we illustrate how secondary compounds behave under typical reaction conditions and how the reaction conditions might affect the stability of the catalyst.