Aqueous-phase Hydrodeoxygenation Of Phenol Over Supported Palladium And Platinum Catalysts

Progressive depletion of petroleum-based fuels has led to the global energy crisis. The greenhouse gas (GHG) emission introduced by burning fossil fuels has made the global warming become one of the biggest environmental challenges in human history. As one of the most significant renewable resources on earth and the only renewable resource to be converted to liquid fuel, biomass has recently received considerable attentions when people search for alternatives of fossil fuel.In contrast to the conventional crude oil, which is a mixture of hydrocarbons containing98wt.%carbon and hydrogen,1.8wt.%sulfur and only0.1wt.%oxygen, bio-oil is an acidic (pH=2.5) aqueous solution containing up to50wt.%oxygen. Bio-oil contains ca.30wt.%of lignin-derived phenolic components (phenols, guaiacols, and syringols) which are of high energy density. Hydrodeoxygenation (HDO) of such phenolic compounds to cycloalkanes has been reported using heterogeneous metal sulfide catalysts at moderate temperatures (573-873K) with high-pressure hydrogen (13-16MPa) in fixed bed reactors. However, the incorporation of sulfur into products over these catalysts stimulated us to develop catalysts, which are not based on sulfides. Combined with supported metal catalysts, water as the main component of bio-oil can act as suitable solvent for the selective hydrogenation or oxidation of the bio-derived chemicals. Water also allows straightforward product separation, if the targeted products are hydrocarbons without polar functional groups.Supported metal catalysts have been widely used for hydrogenation and dehydrogenation reactions because the supports ensure a better dispersion and stability of the metals in addition to influencing their catalytic properties through electronic interactions. Catalysts were characterized by XRD、N2physical adsorption and NH3temperature-programmed desorption.According to the above mentions, many catalysts were designed and prepared in this paper and their catalytic activities were tested using phenol as the model oxygenic compound. After the stability of the reaction at8h, the selectivity of the cyclohexane was Pd/HBeta>Pd/HZSM-5>Pd/MCM-41. The selectivity of the cyclohexane increased as the acidities improved. There is no cyclohexane in the product on Pd/Al2O3、Pd/SiO2. Then we tested that the selectivity of cyclohexane was100%on Pt/HBeta and Pt/HZSM-5. Then the temperature course of the product selectivities of phenol was tested. Selectivity of cyclohexane increased as the reaction temperature rised. The stability in50h was:the selectivity of the cyclohexane decreased with time on supported palladium, and selectivity of the cyclohexane on supported platinum remains stable.