Molybdenum-doped iron phosphate with a M/Fe atomic ratio of 0.04 is found to be effective as a catalyst for a vapor-phase oxidative dehydrogenation of propylene glycol (1,2-propanediol) to pyruvaldehyde (2-oxopropanal, methyl glyoxal). The highest selectivity to pyruvaldehyde was obtained in the temperature range of 175-190 degreesC; the selectivity increased markedly as the concentration of water was increased. Under optimum reaction conditions, the initial selectivity to dehydrogenation was about 60 mol%, but the selectivity decreased a little as the conversion of propylene glycol increased; the selectivity to pyruvaldehyde was 50 mol% at the conversion of 50%. The main side-reaction was the formation of acetaldehyde and formaldehyde by C-C bond fission. Propionaldehyde was also formed with the selectivity of about 10 mol%. (C) 2003 Elsevier Science B.V. All rights reserved.