Preparation And Evaluation Of MoNi/TiO₂SiO₂ Catalysts For Hydrodeoxygenation

With the increasing shortage of oil resources and the continuous severe of the environment,biodiesel is becoming increasingly important as an ideal alternative to oil.At present,catalytic hydrotreating is the most promising technology in the preparation of biodiesel,and the development of catalysts with excellent hydrodeoxygenation activity and hydrothermal stability is at the core of this technology.In this paper,mesoporous TiO₂ and mesoporous SiO₂ were prepared by sol-gel method respectively,the TiO₂SiO₂ was prepared by mechanically mixing,and The TiO₂-SiO₂ were prepared by sol-gel method using ethyl orthosilicate and butyl titanate as chemicals.the NiMo based catalysts were prepared by using TiO₂SiO₂ and TiO₂-SiO₂ composites as supports and were characterized by XRD,BET,SEM and NH₃-TPD,etc.the HDO performance of the catalysts were investigated in the continuous flow fixed-bed reactor using the solution of 20%?vol?jatropha curcas oil+80%?vol?n-octane as the feed and the structure and properties of the catalysts were compared.The effects of the preparation conditions of mesoporous SiO₂,Ti/Si mass ratio,active components loading,Mo/Ni molar ratio,additives kind and amount on the structure of the catalyst and its HDO properties were investigated.The effects of the binder on the catalyst activity,hydrothermal stability and mechanical strength were also examined.As a part of the TiO₂SiO₂ support,the suitable preparation conditions of SiO₂were as follows,CTAB/TEOS molar ratio 0.18,V_NH3?H2O/V_H2O ratio 0.070,V_H2O/V_TEOS ratio 2,water bath temperature 30?,aging time 5h,drying temperature100?,calcination temperature 550?.The SiO₂ obtained under the conditions above has a double mesoporous structure?microporous-mesoporous pore size 2 nm,macroporous pore size 11 nm?and the specific surface area 642.9 m².g^-1.When the mass ratio of TiO₂ and SiO₂ is 0.5,the Ti-Si composite oxide with Ti/Si mass ratio 0.5has a large specific surface area and an ideal double mesoporous structure,and the as–prepared MoNi-based catalyst exhibied excellent hydrodeoxygenation performance.For the hydrodeoxygenation of macromolecular vegetable oil,the catalytic activity of the catalyst is related to the specific surface area and pore structure of the support.The activity of the catalyst and the characterization of the BET,SEM and Py-IR show that TiO₂SiO₂ prepared by the mechanical mixing method is more suitablily used as the catalyst support for the vegetable oil hydrodeoxygenation,and the hydrodeoxidation performance of the MoNi/TiO2SiO2 catalyst is better than that of the MoNi/TiO₂-SiO₂.The TiO₂SiO₂ prepared by mechanical mixing method has the characteristics of bi-mesoporous structure,regular surface morphology,more L-acid centers and the MoNi/TiO2SiO2 with larger pore size,which are all beneficial to improve the hydrodeoxygenation performance of the catalyst.The results show that the catalyst with 25%?MoO3+NiO?mass/support mass and Mo/Ni molar ratio 0.4 exhibited higher hydrodeoxygenation activity.The addition of a certain amount of citric acid?15%of the support mass?could increase the dispersion of the active metals,change the pore structure of the catalyst,and improve the hydrodeoxygenation performance of the catalyst.The MoNi/TiO₂SiO₂ prepared by using aluminum hydroxide as the binder has excellent hydrothermal stability and mechanical stability.The mixture of aluminum hydroxide cement and molecular sieve binder used as binder or the mixture of aluminum hydroxide with adhesive-diatomite used as binder could not improve the hydrothermal stability and mechanical stability of the catalyst,but the former could increase the mechanical strength of the catalyst to a certain extent.