Catalytic Hydrodeoxygenation of Algae Bio-oil over Bimetallic Ni–Cu/ZrO₂ Catalysts

Bio-oil from the catalytic pyrolysis of algae biomass is an attractive energy source. To improve algae bio-oil properties for cofeeding applications in conventional oil refineries, bimetallic Ni–Cu/ZrO2 catalysts, with various Cu/Ni ratios (0.14 to 1.00 w/w) at a fixed total metal loading of 22 wt %, were synthesized and used for hydrodeoxygenation (HDO) of bio-oils via the catalytic pyrolysis of Chlorella and Nannochloropsis sp. at 350 °C and a hydrogen pressure of 2 MPa in a trickle-bed reactor. It was found that the Ni–Cu/ZrO2 catalysts were more attractive than Ni/ZrO2 catalysts in HDO, as the addition of copper could facilitate the reduction of nickel oxide. As the loading of Cu increased, the HDO efficiency of the Ni–Cu/ZrO2 catalyst for crude bio-oil increased and thereafter decreased. The 15.71Ni6.29Cu/ZrO2 catalyst showed the highest activity, with an HDO efficiency of 82% for Chlorella bio-oil. Moreover, the Ni–Cu/ZrO2 catalyst was stable with low sintering and little coking according to transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA) of the catalysts before and after reaction. In addition, this catalyst exhibited the favorable properties of product bio-oils. In particular, the cetane number of the upgraded bio-oil from Nannochloropsis sp. reached the EN 590-09 standard (specification of diesel fuel for vehicles).