Mg- and Ca-modified Ni/SBA-15 catalysts were prepared by incipient wetness impregnation (7 wt% Ni) to be studied for catalytic glycerol steam reforming at 600 degrees C. High space velocities were selected in order to highlight differences in activity between catalysts and deactivation effects at relatively short time. Characterization of the calcined, reduced and used samples was carried out by XRD, ICP-AES, N2physisorption, TGA, H2-TPR, TEM and HCNS elemental analysis. XRD and TEM demonstrated dispersing effect of Mg and Ca on the Ni phase, while TPR evidenced strengthening of the Ni-support interaction by Mg and Ca incorporation to the Ni/SBA-15 catalyst. These effects were significantly noticeable in the Ni/Ca/SBA-15 sample. As a consequence, the Ni/Ca/SBA-15 catalyst achieved the highest glycerol conversion (98.4%) and yield to gases formation (69.9 wt%) with a hydrogen content of 53 vol%. Additionally, this catalyst was stable with time on stream under glycerol steam reforming and showed the lowest coke deposition. This was ascribed to the formation of highly defective carbon deposits, easier to be gasified under reaction conditions, mainly in the form of non-encapsulating carbon nanofibres formed on the small and strongly-supported Ni particles. (C) 2013 Elsevier B.V. All rights reserved.