Abstract
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•Five Ni and/or Cobalt catalysts supported on SBA-15 has been prepared by reduction of highly dispersed nickel/cobalt silicate phases.•Both metals form a bimetallic phase and the presence of nickel improves the dispersion of cobalt metallic phase.•When Co is the main metallic component, a carbide phase is formed during the ethanol reforming reaction.•This carbide phase increases the acetaldehyde production and redisperses the cobalt particles.
In this study, five mono and bimetallic xNi-(10-x)Co/SBA-15 catalysts (x = 10, 8, 5, 2 and 0, with a total metallic content of 10 wt%) have been synthesized using a deposition-precipitation (DP) methodology. Catalytic performances on the steam reforming of ethanol reaction (SRE) have been determined and correlated with their physical and chemical state. A nickel content of 5% or higher yields catalytic systems with good activity, high selectivity to hydrogen and a low production of acetaldehyde (less than 5%). However, in the systems where the cobalt is the main component of the metallic phase (8–10%), the selectivity changes, mainly due to the production of an excess of acetaldehyde, which is also reflected in the larger H2/CO2 ratio. In agreement with previous findings, this important modification in the selectivity comes from the formation of a cobalt carbide phase, where only takes place in the cobalt enriched systems, and is inhibited with nickel content larger than 5%. The formation of this carbide phase seems to be responsible for the decrease of cobalt particle size during the SRE reaction. Even though this cobalt carbide phase is thermodynamically metastable against decomposition to metallic cobalt and graphite carbon, our results have shown that it only reacts and decomposes after a hydrogen treatment at 600 °C.