Preparation Of Ni_xP-ZrP Bifunctional Catalyst And Its Application In Hydrodeoxygenation Of Lignin Bio-oil

Lignocellulose,one of the most abundant biomass resources,has shown great potential in the production of hydrocarbon fuels and high-value chemicals.Lignin accounts for 15?30%of lignocellulosic biomass.The conversion of lignin into bio-oil by rapid pyrolysis or hydrothermal hydrogenolysis is an effective way to produce advanced biofuels.However,lignin bio-oils are mainly composed of oxygen-containing organic compounds which exhibit the shortcomings of low energy density,high viscosity,poor thermochemical stability and low pH value.The deoxygenation of bio-oil is necessary.Hydrodeoxygenation(HDO)is considered to be the most effective method of deoxygenation and upgrading of the bio-oils.Therefore,it is of great significance to prepare highly efficient and stable catalyst for utilizing bio-oil via hydrodeoxygenation.In this work,a bifunctional Ni_xP-ZrP catalyst was prepared by using hydrothermal method.The preparation process variables were optimized based on the influence of Zr/Ni molar ratio and reduction temperature on the catalytic effect was explored.When the Zr/Ni molar ratio is 0.4 and the reduction temperature is 700°C,the catalyst shows the best catalytic activity for the HDO of guaiacol.The composition,acidity,the state of surface elements,morphology and structure of the catalyst was characterized through X-ray diffraction,nitrogen adsorption and desorption test,py-IR,NH₃ temperature-programmed desorption,X-ray photoelectron spectroscopy,scanning electron microscopy and transmission electron microscopy.It is found that the prepared bifunctional catalyst Ni_xP-ZrP-0.4-700 was composed of Ni₁₂P₅ and ZrP₂O₇.It had a shuttle-like morphology with a large number of mesoporous pores distributed on the surface,which showed 67.4 m²/g of surface area,19.8nm of pore size and 0.329 cm³/g of pore volume.The experimental results indicated that there exists electron transfer effect between zirconium and nickel,which gave the catalyst strong hydrogenation activity and acidity,and the total acidity of the catalyst was 0.75 mmol/g.When Ni_xP-ZrP-0.4-700 was used for the hydrodeoxygenation of guaiacol,the conversion of guaiacol reached 97.24%and the yield of cyclohexane reached 95.82%under 3 MPa H₂ at250?for 6 h.After five times of recycling,the activity of the catalyst almost kept the stable.The stability of Ni_xP-ZrP-0.4-700 was highly dependent on anti-toxicity of metal phosphides,high deoxidation activity of the catalyst and strong interaction between Ni₁₂P₅and ZrP₂O₇.According to the distribution of HDO products of guaiacol at different times,a HDO reaction pathway of guaiacol over Ni_xP-ZrP-0.4-700 was proposed.Firstly,the benzene ring of guaiacol was hydrogenated to form 2-methylcyclohexanol.Subsequent demethoxylation gave cyclohexanol though breaking Csp³-OCH₃bond.Finally,the Csp³-OH bond was broken by hydrogenation and the hydroxyl was removed to obtain cyclohexane.The optimal process variables of the hydrodeoxygenation of lignin bio-oil over the bifunctional catalyst Ni_xP-ZrP-0.4-700 were optimized through single-factor experiments.The hydrodeoxygenation products of lignin bio-oil were analyzed by elemental analysis,oxygen bomb calorimetry and GC-MS.When the reaction conditions were under 3 MPa H₂,at 250?for 24 h,a 36.1%carbon yield of alkanes can be obtained.Compared to lignin bio-oils,the main components of the bio-oils after hydrodeoxygenation were alkanes.The oxygen content is reduced from 22.36%of lignin bio-oils to 0.54%,and the calorific value is greatly increased from 27810 k J/kg of lignin bio-oils to 47150 k J/kg,indicating that the Ni_xP-ZrP-0.4-700 catalyst has great potential for catalytic hydrodeoxygenation of lignin bio-oil to produce hydrocarbon fuels.