Previous investigations on the dimerization of n-butenes over Ni-containing Al-MCM-41/ZSM-5 mixed-phase catalysts have shown a correlation between the conversion and the Ni/(Al + Ni) ratio as well as between the conversion and the metal–support interaction, which is represented by the reduction degree. In the present work, both approaches are combined to a novel model parameter, which allows to determine the proportion of active Ni species on the Al-Ni site pairs and thus provides crucial insights into formation of catalytically active nickel sites as well as their effects on the selective formation of low-branched dimers.