Synthesis Of Zeolite Nanoclusters And Modification Of Unsupported NiMo Catalysts

The unsupported NiMo catalyst has high hydrogenation activity,but its low acidity limits its cracking and isomerization activity.In order to compensate for this defect of the unsupported NiMo catalyst,we try to introduce the acidic zeolite nanoclusters into the unsupported NiMo catalyst to increase its acidity and further enhance its cracking and isomerization activity.The ?-zeolite nanoclusters were synthesized by hydrothermal method in the absence of alkali metal ions.The ?-zeolite nanoclusters were combined with unsupported NiMo catalysts by different methods.The composite catalysts were characterized by XRD,BET,SEM,FT-IR,Py-IR,TPD,and HRTEM.It was found that the introduction of ?-zeolite nanoclusters greatly improved the specific surface area,pore volume,and pore size of unsupported NiMo catalysts,which improved the pore structure of unsupported NiMo catalysts.More importantly,the amount of Lewis acid and total acid of the unsupported NiMo catalyst was increased greatly with the introduction of ?-zeolite nanoclusters,and different introduction methods lead to different acid properties of the catalyst.The hydrodesulfurization(HDS)activity results of dibenzothiophene(DBT)showed that the highest activity of hydrodesulfurization and isomerization was obtained by introducing ?-zeolite nanoclusters after synthesis of unsupported NiMo catalyst at 260 °C.In addition,the method changes the desulfurization path of the unsupported NiMo catalyst from the original hydrodesulfurization path(HYD)to the direct desulfurization path(DDS).ZSM-5 zeolite nanoclusters were used to modify unsupported NiMo catalysts.The effects of crystallization time and amount of nanoclusters on the acidity and hydrodesulfurization performance of the unsupported NiMo catalysts were studied.The introduction of ZSM-5 zeolite nanoclusters also increased the amount of Lewis acid and total acid in unsupported NiMo catalyst,but no Br?nsted acid was detected.DBT HDS results revealed that the catalysts Z5-NiMo-5% and Z5-NiMo-14 h exhibited high hydrodesulfurization activity at 280 °C(the desulfurization rate of 98.1% and 100.0%,respectively).In particular,the catalyst Z5-NiMo-5% produced the highest isomerization rate of 68.9% due to more dispersed structure and suitable acidity.Y-zeolite nanoclusters were synthesized in the same way and modified to unsupported NiMo catalysts.The effects of different crystallization time on the acidity and desulfurization activity of unsupported NiMo catalysts were studied.The introduction of Y-zeolite nanoclusters increased the Lewis acid and total acid amount of the unsupported NiMo catalysts.And the hydrodesulfurization activity of the modified catalysts increased first and then decreased with the increase of crystallization time of Y-zeolite nanoclusters at 280 °C,when the crystallization time was 24 h,the highest desulphurization rate was obtained(95.8%).