The vapor-phase reaction of glycerol was performed over a copper-alumina catalyst at ambient hydrogen pressure. Glycerol was converted into 1,2-propanediol (PDO) through dehydration-hydrogenation via hydroxyacetone (HA). We also found that 1,2-PDO was produced at the selectivity higher than 93 mol % in hydrogen flow at gradient temperatures: the dehydrogenation into HA was catalyzed at around 180-200 degrees C, while the following hydrogenation into 1,2-PDO was catalyzed by Cu-alumina catalyst at around 145-160 degrees C.