Synthesis Of Ni-zeolite Bi-functional Catalysts And Their Hydrodeoxygenation Of Phenol In The Liquid Phase

With the dwindling fossil resource and the increasing energy requirements,conversion of phenolics derived from biomass and coal tar into hydrocarbons are considered as one of the most promising strategies to be alternative energy.However,the high oxygen content of phenolic compounds results in undesirable properties with the low energy density,the instability,the low heat-value,etc.,which further prevents their direct application.Catalytic hydrogenation has been considered as one of the most effective methods for upgrading phenolics to hydrocarbons,and the key is catalysts design.In recent years,metal/zeolite bifunctional catalysts have been developed as one of the most promising catalysts.In this paper,a series of Ni/zeolite bifunctional catalysts were synthesized and applied in liquid-phase hydrodeoxygenation of phenol(model compound)to investigate the influence of acidity,porosity and preparation methods of Ni/zeolite bifunctional catalysts on the catalytic performance during phenol conversion,which was anticipated to reveal the relationship between the catalysts properties and their catalytic performance,and even to provide the theoretical support and experimental data for the synthesis of highly efficient catalysts.(1)The Ni dispersibility and particle sizes were proven to be directly related to the crystal sizes of parent zeolites,which further influenced the catalytic performances.The small crystal sizes of parent zeolites were beneficial for dispersing Ni and forming small Ni particles.Ni/HZSM-5(Si/Al=10,25)with the larger crystal sizes and Ni particle sizes showed the weaker catalytic activity.On the contrary,Ni/HZ-5-90 and Ni/HZP-5-90 with the smaller crystal sizes and Ni particle sizes presented the higher catalytic activity.Ni/HZP-5-90 exhibited the highest activity(42.1%)and highest selectivity to hydrocarbons(92.4%)among them,which was also due to the enlarged pores with improving the accessibility of the active sites.(2)Large pore was conducive to the distribution of Ni particles and diffusion,which further influenced phenol hydrodeoxygenation.Ni/HIM-5 presented the highest activity(98.3%)and highest selectivity to hydrocarbons(98.8%)when heated at 220°C in presence of 4.5 MPa H₂ for 1 h.However,it was easily deactivated due to the aggregation of Ni particles and the coverage of organic compounds in this system to active sites.In addition,the high phenol concentration could increase the selectivity of benzene via the direct deoxygenation route.(3)Ni@HZSM-5(Si/Al=100)was synthesized via the encapsulation method and applied in liquid-phase hydrodeoxygenation of phenol.The Ni nanoparticles with about 2?6 nm were uniform distribution in ZSM-5 crystals without any aggregation.Ni@HZSM-5 showed much higher catalytic performance than the impregnated catalyst.Complete conversion of phenol and 100%selectivity of hydrocarbons were achieved over 4 wt%Ni@HZSM-5 encapsulated catalysts,with the outstanding stability during the recycling process.After nine cycles,the phenol conversion and selectivity of alkanes were 100%and 64.6%,respectively.The regenerated 4 wt%Ni@HZSM-5 after nine runs was no obvious variation by TEM,strongly suggesting that Ni nanoparticles possessed excellent stability over Ni@HZSMZ-5 catalyst.It could avoid effectively the migration and aggregation of Ni nanoparticles via the encapsulation effect.