Honeycomb structures loaded with hydrotalcite-derived cobalt catalysts doped with various amounts of Pt and Rh have been tested in the steam reforming of ethanol at 523-823 K under different operational conditions. Catalysts promoted with noble metals are significantly more active than non-promoted hydrotalcite-derived cobalt but, at the same time, they build up carbon very efficiently. Electron microscopy, magnetic measurements and X-ray photoelectron spectroscopy reveal the occurrence of metal cobalt nanoparticles in the samples promoted with noble metals after reaction. According to the TPR profiles recorded over the hydrotalcite-derived cobalt catalysts doped with Pt and Rh, it is concluded that noble metals strongly promote cobalt reduction under ethanol steam reforming (ESR) conditions. Cobalt nanoparticles thus formed are very active for ethanol reforming but, at the same time, they originate severe carbon deposition. In contrast, non-promoted hydrotalcite-derived cobalt catalysts are less active for ESR but do not form carbon due to the absence of metallic cobalt.