Activated carbon-based hybrid Ru catalysts for mild pyrolysis bio-oil stabilization: balancing Ru accessibility and Ru–support interaction

Mild hydrotreating of pyrolysis oil, often referred to as stabilization, requires selective hydrogenation of reactive oxygenates while limiting cracking, decarboxylation, and coke formation. This balance depends on how catalyst support controls Ru accessibility and Ru–support interaction. Here, 5 wt% Ru catalysts were prepared on activated carbon (AC) and AC-based hybrid supports containing TiO₂, ZrO₂, Al₂O₃, or ZSM-5 to identify a support design window that promotes stabilization while limiting carbon loss. CO chemisorption, H₂-TPR, XPS, BET, and STEM–EDS showed that support composition changed accessible Ru dispersion, reducibility of oxidic Ru species, and local Ru–oxide association. Pyrolysis oil diluted with n-butanol was hydrotreated at 200 and 250 °C. At 200 °C, catalysts favored stabilization, giving higher H/C ratio, lower micro carbon residue, and improved carbon retention. At 250 °C, higher deoxygenation was accompanied by increased CO₂ formation, hydrogenolysis/cracking, lower liquid yield, and higher micro carbon residue. Ru/AC–ZrO₂ showed the best balance, achieving about 60 wt% deoxygenation with comparatively high liquid yield, carbon retention, and low micro carbon residue. These results show that effective stabilization depends on a balance between Ru accessibility and Ru–support interaction, rather than on Ru dispersion alone.