(510d) Catalytic Hydroprocessing of Fast Pyrolysis Bio-Oil Model Compounds

    Catalytic hydroprocessing of fast pyrolysis bio-oil to produce transportation fuel has attracted much attention in recent years due to the diminishing fossil fuel resources. Given that bio-oil is a complex mixture containing over 300 compounds, hydroprocessing of real bio-oil could involve hundreds of reactions. Model compound studies can reduce the complexity and allow a better understanding of the reaction mechanisms. In this talk, we will present the results of systematic evaluation of various noble metal catalysts with respect to hydroprocessing of model bio-oil substrates such as p-cresol, acetic acid and furfural, as well as the binary and ternary combinations of these compounds. As an example, for hydroprocessing of acetic acid as a model carboxylic acid, Ru/C catalyst shows the highest activity among the tested catalysts (including Pt, Pd, Ru on either C or Al₂O₃ support). Further, although hydrogenation of acetic acid to ethanol is favored at lower temperatures and higher H₂ pressures, the selectivity to CH₄ remains high in all reactions with water as a solvent, attributed to rapid hydrogenolysis of ethanol to CH₄. However, with n-heptane as a solvent, ethanol hydrogenolysis appears to give way to esterification leading to ≥60% selectivity to ethyl acetate. In addition, the results with binary combination of acetic acid and p-cresol on Ru/C catalyst indicated that the hydrogenation of acetic acid is suppressed by the presence of p-cresol. In sharp contrast, the presence of acetic acid promotes the HDO of p-cresol by dehydration reaction, leading to high selectivity to methylcyclohexane. Such a comprehensive understanding is essential to rationally develop novel multi-functional catalysts and processing strategies for effective deoxygenation of bio-oils.