Sources of deactivation during glycerol conversion on Ni/gamma-Al2O3

Hydrogenolysis of glycerol was studied using a diluted aqueous solution of glycerol in gas phase and atmospheric pressure on Ni/¿-Al2O3 catalyst. The catalytic transformation of glycerol generates products derived from dehydration, dehydrogenation, hydrogenolysis and condensation reactions. Deep hydrogenolysis route to produce CH4 prevails in the first few hours of reaction. As the reaction time progress, dehydration-dehydrogenation products start to appear. Here, a description of the deactivation sources and its effects on the catalytic performance of Ni catalyst was proposed. The catalyst was characterized before and after the catalytic reaction by high-resolution transmission electron microscopy (HRTEM) and by employing Fourier transformed infrared spectroscopy (FTIR) of adsorbed CO. A source of deactivation was due to carbonaceous deposition. FTIR at low CO dosing pressure reveal bands assignments species essentially due to linear and bridge carbonyls, whereas high pressure CO dosing produces a complex spectra due to polycarbonyls. X-ray absorption near edge structure (XANES) analysis was employed to reveal the initial degree of reduction of the fresh catalyst. The oxidation of metallic Ni in the course of reaction may also be considered as a source of deactivation. Ni oxide species promote dehydration routes. Alumina support facilitates nickel species to be more active toward interacting with glycerol. Dehydration, which takes place on the acid sites, is the mainly route related to the generation of carbon deposition and to the observed catalyst deactivation. Another source of deactivation was due to carbiding of Ni to form Ni3C. The regeneration of used Ni catalyst was achieved by oxidation-reduction steps at 723 K.
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