The aim of this work was to probe for the first time the back-spillover of labile 0 and OH species during steam reforming of phenol towards H-2 production over Rh and Fe supported on MgO, Mg-Ce-O and Mg-Ce-Zr-O metal oxides. This was made possible through SSITKA and other transient isotopic experiments (use of D2O and O-18(2)). The size of the active pool of H-containing species (H and/or OH) present under reaction conditions as a function of reaction T and catalyst composition, and deuterium kinetic isotope effects were measured. (c) 2005 Elsevier B.V. All rights reserved.