The conversion of glycerol in gas phase and atmospheric pressure has been investigated over 10 wt.% Ni/γ-Al2O3 catalyst. The catalysts were prepared with nickel nitrate and pre-treated with hydrogen in the range of 623–1073 K. The resultant catalysts were characterized by N2-physisoption, H2-chemisorption, X-ray diffraction (XRD), TGA-MS, TEM, RAMAN, NH3-TPD, XPS, TPO-MS and XANES. The stability and the catalytic behavior of the catalysts were affected by the reduction pre-treatment. Glycerol reaction pathways were proposed based on dehydration, dehydrogenation and hydrogenolysis steps. The main products identified were: hydroxyacetone, pyruvaldehyde, pyruvic acid, lactic acid, lactide, acetaldehyde and methane. The number of exposed Ni atoms and the degree of reduction of the NiO species affected the hydrogenolysis reaction of glycerol to CH4 affecting the catalytic stability. The catalyst was deactivated by coke formation, by transformation of Ni phase to nickel carbide (Ni3C), as well as by oxidation of the Ni phase during the reaction. In addition, Raman analysis revealed two types of carbonaceous deposits over the used samples: on the Ni species and on the support. The regeneration treatment by oxidation–reduction reactivated the catalyst successfully.