Decomposition of ethanol into H2-rich gas and carbon nanotubes over Ni, Co and Fe supported on SBA-15 and Aerosil

SBA-15 with a 2D hexagonal mesoporous structure exhibiting a narrow pore size distribution and commercial AEROSIL380 silica were used as supports for the dispersion of Ni, Co or Fe metal oxide particles. After reduction at 973 K, catalytic properties of these materials were evaluated for ethanol conversion to H-2 and carbon nanotubes (CNTs). The reduced composites were selective for hydrogen production as follows: iron (45-55%) < cobalt (55-70%) < nickel (70-80%) regardless of the type of silica used as support. The nickel-based catalysts appeared to be the most active for the production of hydrogen and also generate carbon nanotubes in large amounts, independently of the support porosity. HRTEM micrographs showed a generally well-defined morphology and a quite uniform outer diameter of CNTs produced using the Ni composites. The texture of the silica support had however a particular influence on the catalytic properties of the cobalt-based catalysts. Both Ni and Co supported on SBA-15 silica generate a mixture of CNTs and carbon nanofibers (CNFs) with a wider size distribution compared with that of the CNTs produced over Ni/Aerosil. This lack of selectivity was attributed to the expelling of Co particles from the SBA-15 mesoporous channels upon reduction. All Fe/silica materials proved the least active and selective. Along the major carbon fibers, they generate a few poorly defined multi-walled CNTs with small diameter. TG analysis indicated that all CNTs exhibit a relative high stability in an oxidizing atmosphere. (C) 2015 Elsevier B.V. All rights reserved.