Carbon deposition on bimetallic Co–Ni/Al2O3 catalyst during steam reforming of glycerol

This paper reports the nature and kinetics of carbon deposition on bimetallic Co–Ni/Al2O3 catalyst during the steam reforming of glycerol. Reaction runs were carried out under stoichiometrically excess steam conditions between 773 and 823 K. Total organic carbon content of used catalysts varied between 18 and 30 wt.%. Carbon deposition occurred on the calcined Al2O3 support probably due to the presence of weak acid centres. Thermogravimetric analysis revealed two types of carbonaceous pools on catalyst surface—a relatively smaller deposit reactive with both H2 and O2 and a larger reservoir that could only be gasified with O2. Gas composition analysis showed that only CH4 and H2O were produced during H2-TPR while CO2 and H2O were produced during TPO. FTIR characterisation confirmed the presence of C–O, C–C, C–H, O–H and CC bonds in the carbon residue. Carbon deposition rate has an order of 0.55 with respect to glycerol partial pressure and order of −0.22 for steam. Indeed, a Langmuir–Hinshelwood kinetic model involving dissociative adsorption of glycerol and molecular chemisorption of steam adequately captured the carbon deposition rate behaviour. Catalyst regeneration using a TPO–TPR–TPO–TPR scheme restored the physicochemical properties to the same level as the fresh catalyst.