The activities and selectivities in the hydrogenation of acetonitrile on catalysts obtained from Ni/Al and Ni/Mg/Al layered double hydroxides (LDHs) precursors depend on the nature of their compensating anions: CO32-,NO3- or Cl-. The latter gives rise to sample with low activity and the less selective to primary amine. Studies by XRD, TG-DSC, mass spectrometry and TPR experiments show that the anion influences the thermal stability and the reducibility of the Ni-containing LDHs. The thermal decomposition of LDH into the mixed oxide form involves the dehydration, then the dehydroxylation of the layers with the concurrent decomposition of CO32- and NO3-which occurs at similar temperature in air or H-2 atmosphere. In TPR experiments the reduction of Ni2+ to Ni-0 takes place at above 800 K. A specific behaviour is observed when Cl- is the compensating anion, with a better reducibility of Ni2+ and the existence of Ni species reduced at low temperatures, not observed with CO32- and NO3- as anions. In addition, all the mixed oxides are poorly reconstructed in water, and a clear segregation of bayerite occurs on the chloride samples. This last phenomenon is enhanced in the Mg-containing compound. It is proposed that the presence of both Cl and Mg favours the extraction of aluminium and makes the accessibility to a significant amount of Ni2+ cations easier, thus increasing their reducibility. In this case, Ni-0 particles with an average size around 65 nm are detected after reduction at 723 K, while the other samples, poorly reduced, still contain the mixed oxide structure.