The effect of catalyst preparation methods on biomass hydrothermal liquefaction: Exploring cleaner and more efficient pathways for catalytic hydrothermal liquefaction of biomass

• Hydrothermal precipitation enhances biomass liquefaction efficiency more than impregnation. • Fe-Ni 2 /CeO 2 catalyst yields 39.8% bio-oil and 32.7% hydrothermal carbon conversion. • Ni 2 /CeO 2 enhances bio-oil quality with an O/C ratio of 0.22 and HHV of 30.73 MJ/kg. • Hydrothermal catalyst significantly reduce oxygen level and enhance bio-oil quality. • The hydrothermally prepared catalyst outperforms the impregnation method catalyst. In order to study the impact of different catalyst preparation methods on the biomass hydrothermal liquefaction (HTL) process, this research aims to provide more efficient and sustainable catalyst preparation strategies for biomass hydrothermal liquefaction technology. Catalysts were synthesized using both traditional impregnation and hydrothermal precipitation methods to evaluate their effects on the conversion of bio-crude oil, solid residue, and gas composition. The findings indicated that the hydrothermal precipitation method had superior activity in converting bio-crude oil, with the Fe-Ni 2 /CeO 2 catalyst achieving conversion rates of 39.8 % for bio-crude oil and 32.7 % for solid residue. The quality of the bio-crude oil, as determined by elemental analysis, revealed that under the influence of Ni 2 /CeO 2 , the maximum O/C ratio and the higher heating value (HHV) were 0.22 and 30.73 MJ/kg, respectively. Further Electron Paramagnetic Resonance (EPR) analysis showed that although hydrothermal precipitation led to partial retention of active metals in the aqueous phase, this method generated a significant number of oxygen vacancies. The highest concentration of oxygen vacancies in Fe-Ni 2 /CeO 2 was found to be 2.369 × 10 13 spins/g. These oxygen vacancies are beneficial for water adsorption, aiding proton hopping on metal oxide surfaces, thereby enhancing the catalytic hydrodeoxygenation. This results in a lower oxygen content in the catalyst and improved quality of bio-crude oil.