The aim of this work was to probe the back-spillover of labile O, OH and H species during steam reforming of phenol towards H-2 production in the 773-1028 K range over Rh supported on MgO and Mg-Ce-Zr-O mixed-metal oxides. This was made possible through steady state isotopic transient kinetic analysis (SSITKA) and other transient isotopic experiments (use of D2O and O-18(2)) combined with temperature-programmed desorption ones. The size of the active pool of H-containing intermediate species (H and/or OH) present in the H-path of reaction as a function of reaction T was measured over the 0.1 wt% Rh/50Mg-25Ce-25Zr-O catalyst by SSITKA experiments. It was found that the size of this pool decreases by 18% in the 773-928 K range (theta = 68.9-56.3), whereas a significant decrease (by a factor of 10) was observed between 928 and 1028 K. These results demonstrate that most of the active H and OH species reside on the support and metal-support interface. Two kinds of H-containing intermediate species are likely to participate in the H-path of reaction. An inverse D kinetic isotopic effect was measured for the H-2 formation in the phenol steam reforming reaction in the 773-1028 K range. (C) 2006 Elsevier B.V. All rights reserved.