Preparation And Evaluation Of MoNi/MgAl₂O₄ Catalysts For Hydrodeoxygenation

Biodiesel with excellent properties can be produced via hydrodeoxygenation technology,used vegetable and animal oil as feed. The key to promote the industrialization process of biodiesel is to develop new type catalysts with excellent hydrodeoxygenation activity and hydrothermal stability. Magnesium aluminate spinel（MgAl₂O₄） with excellent hydrothermal stability were prepared by the co-precipitation and sol-gel method in this paper, MoNi/MgAl₂O₄ catalysts were obtained by loading activity component on the magnesium aluminate spinel support for hydrodeoxygenation（HDO）. Using vegetable oil as feed, the effects of the MgAl₂O₄ preparation conditions on HDO performance of the catalysts were systematically investigated; the effects of the MoNi/MgAl₂O₄ and MoNi/γ-Al2O3 catalysts on HDO performance and hydrothermal stability were also studied.As the carrier of vegetable oil HDO catalysts, MgAl₂O₄ were prepared by the co-precipitation method using CTAB as surfactant and ammonia water as precipitant agent,the suitable preparation conditions were as follows: CTAB / Mg molar ratio 0.180, pH 10.6,bath temperature 80 ℃, aging time 1h, drying temperature 120 ℃, Al（NO3）3·9H2O :Mg（NO3）2·6H2O ratio 2:1, calcination temperature 700℃; MgAl₂O₄ were prepared by the sol-gel method using CA as complexing agent, the suitable preparation conditions were as follows: Mg/Al molar ratio 0.5, C2H5OH/H2 O volume ratio 1.0, pH 1.0, calcination temperature 800℃,（Mg + Al）/CA molar ratio 1.0. MgAl₂O₄ prepared under above conditions have high purity, the average pore size of MgAl₂O₄ were prepared by the co-precipitation method was about 20.0 nm, and the average pore size of MgAl₂O₄ were prepared by sol-gel method was about 12.2 nm, the larger pore size in carrier is contribute to the contact between macromolecules vegetable oil with large molecular weight and active ingredients on catalysts.The results of HDO performance on the catalysts and characterizations of BET 、NH3-TPD etc. on MgAl₂O₄ and γ-Al2O3 show that for the hydrodeoxygenation of vegetable oil with large molecular weight, the amount of acid and the specific surface area have little affect on the catalytic activity of the catalyst, while the pore size of the support is a main factor affecting the catalytic activity on the catalysts, the catalysts with larger pore size in the support have higher catalytic activity.The results of HDO performance on the catalysts before and after hydrothermal treatment show that compared with the MoNi/γ-Al2O3 catalyst, the MoNi/MgAl₂O₄ catalystexhibited excellent catalytic activity and hydrothermal stability. The XRD characterizations of the catalysts before and after hydrothermal treatment show that the supports γ-Al2O3 were generated to MoO2 and AlNi3 in the reaction with Mox Niy, which led to irreversible decline of the catalytic activity, while the MgAl₂O₄ had excellent hydrothermal stability;Compared with the MoNi/γ-Al2O3 catalyst, the MoNi/MgAl₂O₄ catalyst has littleγ-Al2O3（about only 22wt% of supports）, so that hydrothermal treatment has little effect on HDO performance of the MoNi/MgAl₂O₄ catalysts.The HDO catalysts supported on the MgAl₂O₄ exhibited excellent catalytic activity and hydrothermal stability in the reaction environment, in 133 h running time, the average HDO of hydrogenated oil is more than 99.0%.