Effect of addition of rhenium was investigated during catalysis of TiO2-supported Rh and Ir metals for aqueous phase reforming of ethanol. By adding Re to Rh/TiO2 and Ir/TiO2 catalysts, the initial rates of H-2, CH4, and CO2 formation increased 3-4 times, together with the extraordinary increase of acetic acid formation. Detailed mechanisms of the reforming reaction were investigated using various physicochemical techniques. The role of added Re was the acceleration of the hydration of acetaldehyde to form acetic acid rather than the decomposition of acetaldehyde to form CH4 and CO on both Rh/TiO2 and Ir/TiO2 catalysts. Well dispersed bimetallic nano-composites would work as the active sites for ethanol dehydrogenation and acetaldehyde decomposition, whereas partially oxidized ReOx sites may work for the hydration of acetaldehyde to form acetic acid. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.