Coke evolution in simulated bio-oil aqueous fraction steam reforming using Co/SBA-15

Abstract

This paper studies Co/SBA-15 catalyst deactivation during the steam reforming of model compounds from the aqueous fraction of bio-oil coming from biomass HTL. We observed how deactivation took place in two clearly differentiated stages. In the first one (TOS 20 h), where conversion decreased strongly, Co sintering deduced from XRD and, pore blockage by coke deposition were observed. At this first stage, coke seemed to be filamentous and some encapsulated Co particles could be appreciated by TEM. The encapsulating coke reduced the number of accessible centers to catalyze the reforming reaction. In the second stage (TOS 20 h), filamentous coke was also observed but more condensed and therefore more aromatic, as verified by higher C/H ratio determined by elemental analysis. In this stage, despite the amount of coke deposited was growing, no drop on specific surface area was observed. Besides, since no peaks corresponding to cobalt oxides were detected in the XRD patterns, catalyst deactivation cannot be attributed to metallic active sites oxidation. The t-Student statistical analysis showed that Co/SBA-15 catalyst deactivation is mainly affected by the amount of coke deposited and its C/H ratio.