It was investigated the lactic acid (LA) production from glycerol in alkaline medium (NaOH) employing platinum (0.5 wt% PtO2) catalysts supported on Al2O3, ZnO and MgO in continuous flow reaction system over a period of 30 h. Besides the effect of catalyst supports, it was studied the influence of the temperature/pressure and NaOH/glycerol molar ratio. The catalysts were prepared by incipient wetness method and characterized by XRF, XRD, N-2 adsorption-desorption, TPR, TPD-CO2 and the dispersion of platinum was determined by H-2 chemisorption. The reactions were performed at 200-260 degrees C, 20-46 atm, with space velocity (WHSV) of 211-1,10 vol% glycerol solution and NaOH/glycerol molar ratio of 0.5, 0.75 and 1.0. The results of the catalytic tests showed that the main liquid products are lactic acid and 1,2-propanediol (1,2-PDO). Using the Pt/ZnO catalyst at 240 degrees C/35 atm and NaOH/glycerol molar ratio = 1, it was obtained the highest lactic acid selectivity (similar to 80%) and yield (similar to 68%). However, in this reaction, the lactic acid yield decreases to around 25% if NaOH/glycerol molar ratio is reduced to 0.5. The highest yield to 1,2-propanediol (18.5%) was obtained with Pt/Al2O3 catalyst that was associated with the acidity of the catalyst. The catalysts showed excellent stability without evidence of deactivation over the evaluated period. (C) 2017 Elsevier Ltd. All rights reserved.