  We investigate the electronic reconstruction in
(LaNiO$_{3}$)$_n$/(LaAlO$_{3}$)$_3$ (n=3, 5 and 10) superlattices due to the
quantum confinement (QC) by d.c. transport and resonant soft x-ray absorption
spectroscopy. In proximity to the QC limit, a Mott-type transition from an
itinerant electron behavior to a localized state is observed. The system
exhibits tendency towards charge-order during the transition. ab initio cluster
calculations are in good agreement with the absorption spectra, indicating that
the apical ligand hole density is highly suppressed resulting in a strong
modification of the electronic structure. At the dimensional crossover cellular
dynamical-mean-field calculations support the emergence of a Mott insulator
ground state in the heterostructured ultra-thin slab of LaNiO$_{3}$.
