To promote long-term stability of Pt/CeO2 catalyst for ethanol steam reforming, two approaches were examined. Sn was added to Pt to suppress carbon formation. Although the catalyst with high Sn content exhibited improved stability, acetaldehyde selectivity was prohibitive. DRIFTS experiments revealed that Sn inhibited the ability of Pt to facilitate steam-assisted forward acetate decomposition reaction to carbonate, the precursor to CO2 formation. However. CO2 co-feeding was more effective, not only in promoting long-term catalyst stability, but also in maintaining high H-2 selectivity. DRIFTS experiments indicate that the kinetic influence of CO2 can be explained as a competition with ethanol for adsorption sites, leading to a suppression in the rate of formation of coke precursors. (C) 2010 Elsevier B.V. All rights reserved.