Gas-phase hydrodeoxygenation of guaiacol over iron-based catalysts. Effect of gases composition, iron load and supports (silica and activated carbon)
Résumé
Fe/SiO2 is shown to be a selective catalyst for guaiacol hydrodeoxygenation (HDO). Guaiacol is used as a model compound to study the conversion of lignin pyrolysis vapours into aromatics (benzene, phenols). The effect of each individual gas present in a pyrolysis gas (H2, CO, CO2, H2O, CH4) on the selectivity of a 10wt% Fe/SiO2 catalyst is studied (673K, atmospheric pressure, 50mol% H2, 1/WHSV=0.6gcath/ggua). The speciation of the iron phase (metallic (α-Fe), carbide (Fe5C2), oxide (Fe3O4), and super-paramagnetic) in spent catalysts is revealed by XRD and Mössbauer spectroscopy as a function of gases composition. At least 3 types of carbonaceous deposit were evidenced by TPO analysis. TEM observations showed that iron particles size is not markedly affected by the reaction and that carbon deposit mainly occurs in the vicinity of iron particles. When all the gases except methane (Guaiacol+H2+CO+CO2+H2O) are simultaneously in the feed stream, the conditions are still sufficiently reducing to maintain the activity of the catalyst (66% of benzene and toluene carbon yield, 7.5gcath/ggua). The effects of support (silica or activated carbon-AC) and iron loading (5, 10, 15wt% Fe/SiO2) were also studied. 10wt% Fe/AC has a higher selectivity in phenol and cresols production than Fe/SiO2. Active sites and reaction mechanisms are discussed.
Mots clés
Biorefinery
Chemicals
Hydrotreatment
Lignin
Active site
Aromatic
Benzene and Toluene
Biorefineries
Carbon deposites
Carbon yield
Carbonaceous deposits
Feed streams
Gasphase
Hydrodeoxygenation
Iron loading
Iron Particles
Iron-based catalyst
Lignin pyrolysis
Model compound
Reaction mechanism
Selective catalysts
Spent catalyst
Ssbauer spectroscopies
TEM observations
XRD
Activated carbon
Alcohols
Atmospheric pressure
Benzene
Carbides
Carbon dioxide
Catalyst activity
Deposits
Gases
Iron
Metallic compounds
Methane
Molybdenum oxide
Paramagnetism
Phenols
Silica
Toluene