Evaluating niobia-supported Ni-Fe catalyst for hydrodeoxygenation (hdo) of lignin-derived pyrolysis oils

Abstract

Hydrodeoxygenation (HDO) of lignin-derived pyrolysis oils presents a promising pathway for producing renewable, low-carbon liquid fuels. This thesis evaluates the performance of niobium oxide (Nb₂O₅)-supported catalysts in both batch and continuous HDO processes, comparing them with silica-supported catalysts to assess the role of the support in catalytic performance. The study focused on Ni-Fe bimetallic catalysts, investigating the interaction between the two metals and the support to optimize deoxygenation efficiency. In the batch HDO of guaiacol, the 5Ni1Fe/Nb₂O₅ catalyst exhibited the best performance, achieving high selectivity towards cyclohexanol and cyclohexane, emphasizing the synergistic effect between Ni and Fe and the role of Nb₂O₅ acidity in promoting hydrogenation and deoxygenation. In contrast, the 5Ru/Nb₂O₅ catalyst showed the highest conversion rate (55%), but with a preference for hydrogenation rather than complete deoxygenation. For bio-oil HDO, the 5Ni5Fe/Nb₂O₅ catalyst emerged as the most effective, demonstrating moderate hydrogen consumption, low CO₂ production, and efficient deoxygenation. Its ability to balance oxygen removal while retaining carbon makes it a strong candidate for practical bio-oil upgrading. In the continuous reactor HDO tests, the 5Ni1Fe/Nb₂O₅ and 5Ru/Nb₂O₅ catalysts were synthesized using Nb₂O₅ in pellet form to enhance mechanical stability for scale-up. Both catalysts exhibited a tendency toward hydrogenation, with 5Ni1Fe/Nb₂O₅ confirming its superior performance in deoxygenation, validating findings from batch studies and reinforcing its potential for industrial application in sustainable biofuel production.