Synthesis Of New Three-dimensional KIT-5 Based High-efficiency Catalyst And Its Hydrodenitrogenation Performance

With the increasingly strict environmental protection requirements,the quality requirements for fuel products are becoming more strict than before,so the S and N contents in oil products require much lower.Although the total content of N in the petroleum fraction is usually less than S,nitrogen-containing compounds coexisting with other non-hydrocarbon compounds make the stability of oils deteriorous;furthermore,nitrogen-containing compounds are preferentially adsorbed on the acid centers of catalysts making them poisoned and deactivated;moreover,the existence of a trace amount of nitrides will inhibit hydrodesulfurization and hydrodearomatization.Therefore,hydrodenitrogenation technique has attracted more and more attention from scientific researchers.Mesoporous material of KIT-5 has high specific surface area(nearly 1000 m²/g)and pore volume(0.8?1.0 cm³/g),and three-dimensionally ordered open channels,which endow it good application prospects in the fields of adsorption and separation.However,compared with the traditional microporous molecular sieve materials,KIT-5material has silicous skeleton and amorphous pore wall,thus resulting in a poor hydrothermal stability and a weak acidity,which significantly limits its industrial application.Therefore,how to improve the acidity and hydrothermal stability of KIT-5material is one of the important problems for expanding the practical performance.Thus,this thesis mainly focuses on the framework modification of KIT-5 material with heteroatoms and on the pore construction by embeding microporous zeolite structural units into the wall,based on the XRD,FT-IR,TEM,Raman,XPS and other technical means to analyze and characterize the series of materials and catalysts;quinoline was used as the model compound to evaluate the hydrodenitrogenation performance of the catalysts,and the inhibitory effect of quinoline on the removal of dibenzothiophene on the catalyst was explored.The main findings in this research are as follows:(1)A series of Ti-KIT-5 materials with different Si/Ti ratios were synthesized using F127 as template by in-situ modification method.The small angle XRD and TEM results proved that the modified Ti-KT-x(x>10)materials couldretain the ordered mesoporous channels.FT-IR results illustrated that Ti species were successfully embedded into the framework of mesoporous KIT-5 material.The modified Ti-KT-x and pure KIT-5 materials were used as supports to prepare Ni Mo supported catalysts for quinoline hydrodenitrogenation.The activity results showed that the Ni Mo/Ti-KT-20catalyst exhibited the highest quinoline hydrodenitrogenation activity and the highest(PCHE+PCH)/PB selectivity(2.83).Compared with other catalysts,Ni Mo/Ti-KT-20catalyst had the highest k _HDN(3.94×10^-4mol g^-1h^-1)and TOF values(10.6×10^-1h^-1).(2)ZSM-5-KIT-5(ZK)materials with different addition amounts of ZSM-5crystallinities were successfully synthesized by a nano self-assembly method,and were employed as supports to prepare hydrodenitrogenation catalysts.The characterization results of XRD and FT-IR demonstrated that the ZK materials possessed both mesoporous structure and MFI structure,indicating that ZSM-5 structure units were fabricated into the framework of the KIT-5 material.With the usage of a ZSM-5 seed solution,the wall thicknesses of the composite materials were gradually enhanced,leading to slight decreases in the pore sizes,specific surface areas and volumes of the ZK materials.Furthermore,the addition of ZSM-5 emulsion strengthened the acidic properties and produced more Br?nsted acid sites.The performances of all the catalysts were evaluated for quinoline hydrodenitrogenation.Among all the catalysts,Ni Mo/ZK-3 showed the highest HDN efficiency(79.3%),the maximum k _HDN(3.47×10^-4 mol g^-1 h^-1)and a high ratio of(PCHE+PCH)/PB(4.13).(3)Based on the ZK composite materials prepared in the previous chapter,trimetallic Ni Mo W/ZK series catalysts with different Mo/W ratios were prepared by the step-by-step equal volumetric impregnation method.The XRD characterization results indicated that the series of Ni Mo W/ZK catalysts maintained the characteristic structure of mesoporous materials and microporous molecular sieves.TPR results indicated that the interaction between the supports and the active metal was continuously enhanced as the Mo metal was continuously replaced by the W metal.Using quinoline as the feed,the hydrogenation activity of the series of catalysts was evaluated.Compared with other catalysts,the 3Ni Mo W/ZK catalyst showed the best hydrodenitrogenation activity(90.67%)and the highest(PCHE+PCH)/PB selectivity(5.03).(4)Beta-KIT-5(BK)composite materials with different Si O₂/Al₂O₃ ratios were synthesized by two-step crystallization method.BK composite material had the structural characteristics of KIT-5 mesoporous material and Beta microporous molecular sieve.Ni Mo W supported catalysts were prepared using Beta,KIT-5 and BK materials with different Si O₂/Al₂O₃ ratios as support,and the corresponding hydrogenation performance of the series catalysts was evaluated using quinoline and dibenzothiophene as raw materials.Compared with other catalysts,Ni Mo W/BK-3catalyst had the best hydrodenitrogenation activity(93.6%)and hydrodesulfurization activity(99.1%).In addition,the effect of quinoline on the removal of dibenzothiphene on the catalysts was investigated.The results showed that the hydrodenitrogenation reaction on the Ni Mo W/BK-3 catalyst had the smallest inhibition effect on the hydrodesulfization reaction,which was attributed to its unique pore structure,suitable acid sidtribution and high B/L ratio value,moderate Mo(W)S₂ active phase distibution.