Gas-phase hydrodeoxygenation of guaiacol over iron-based catalysts. Effect of gases composition, iron load and supports (silica and activated carbon)

Abstract Fe/SiO 2 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 (H 2 , CO, CO 2 , H 2 O, CH 4 ) on the selectivity of a 10 wt% Fe/SiO 2 catalyst is studied (673 K, atmospheric pressure, 50 mol% H 2 , 1/WHSV = 0.6 g cat  h/g gua ). The speciation of the iron phase (metallic (α-Fe), carbide (Fe 5 C 2 ), oxide (Fe 3 O 4 ), and super-paramagnetic) in spent catalysts is revealed by XRD and Mossbauer 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 + H 2  + CO + CO 2  + H 2 O) 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, 7.5 g cat  h/g gua ). The effects of support (silica or activated carbon-AC) and iron loading (5, 10, 15 wt% Fe/SiO 2 ) were also studied. 10 wt% Fe/AC has a higher selectivity in phenol and cresols production than Fe/SiO 2 . Active sites and reaction mechanisms are discussed.