Catalytic Upgrading of Bio-oil over Ni-Based Catalysts Supported on Mixed Oxides

Ni-Based catalysts using mixed oxides of Al2O3-SiO2, Al2O3-TiO2, TiO2-SiO2, and TiO2-ZrO2 as supports were evaluated for hydrotreatments using guaiacol as the model compound and characterized by N-2 physical adsorption, X-ray diffraction (XRD), temperature-programmed desorption of ammonia (NH3-TPD), and temperature-programmed reduction of hydrogen (H-2-TPR) techniques. The influence of the support, solvent, reaction temperature, and pressure on guaiacol conversion and product distributions were determined. Guaiacol conversion of 100% with cyclohexane selectivity of 86.4% was obtained over the Ni/TiO2-ZrO2 catalyst at the conditions of 300 degrees C, 4.0 MPa H-2 pressure, and decalin solvent. Furthermore, this system is also efficient for real bio-oil, where nearly 19.3% of the upgraded bio-oil yield was achieved under the optimal conditions determined for guaiacol. Gas chromatography-mass spectrometry (GC-MS) analysis showed that the principal components were phenolic compounds, while the content of acids and aldehydes was negligible. The pH of bio-oil increased from 2.38 to 4.21, and the high heating value drastically increased from 13.1 to 25.8 MJ/kg.