Ab initio density functional theory calculations have been performed to investigate the catalytic role of water molecules in the oxidation reaction of ethanol: CH3CH2OH+nH(2)O-->CH3CHO+H-2+nH(2)O (n=0, 1, 2). The results show that the potential energy barrier for the reaction is 88.0 kcal/mol in case of n=0, while it is reduced by similar to34 kcal/mol when two water molecules are involved (n=2) in the reaction. As a result, the rate constant increases to 3.31x10(-4) s(-1), which shows a significant catalytic role of water molecules in the ethanol oxidation reactions. (C) 2002 Elsevier Science B.V. All rights reserved.