The effects of the alkali addition (e.g., Li, Na, K) on the physico-chemical properties of a 19% Ni/MgO catalyst (alk(at)/Ni-at = 0.122 divided by 0.150) have been evaluated by TPR, TPD of H-2 (H-TPD) and CO (CO-TPD), TEM and temperature-programmed reaction measurements in toluene hydrogenation (TPTH). Lithium promotes the reduction negatively affecting the morphology and dispersion of the Ni/MgO catalyst, whereas both Na and K enhance the development of the active surface area, Alkali exert a physical effect on the active phase which lowers both the CO chemisorption stoichiometry acid the sticking coefficient of toluene hydrogenation, Alkalis also induce an electronic effect on the active Ni phase resulting both in the inhibition of the Bouduard reaction (2 CO(ads) --> C-(ads) + CO2) and in a drop (approximate to 20 kJ mol(-1)) of E-app in toluene hydrogenation.