Redox phase unpromoted molybdenum catalysts with different Mo loadings (2.5% Mo/γ-Al 2 O 3 ; 5.0% Mo/γ-Al 2 O 3 ; 7.5% Mo/γ-Al 2 O 3 and 10.0% Mo/γ-Al 2 O 3 ) were prepared and characterized for the ammoxidation of glycerol to nitriles, such as acrylonitrile. The best catalyst (10.0% Mo/γ-Al 2 O 3 ) obtained a yield of 26% in nitriles. The increase in the molybdenum content and its oxidation states along with the amount of weak/moderate acid sites on the support surface are key points for the optimization of the catalysts.