Synthesis And Catalytic Properties Of Functionalized Hierarchical Porous Materials

With the rapid development of the national economy,oil,as an extremely important energy source,grasps the lifeline of economic development and is receiving more and more attention from all countries.Most of the petroleum products widely used in the world are light oils with lower boiling points.Heavy oils are characterized by high viscosity,high density,high asphalteneity,high resin,high sulfur and high nitrogen content,so heavy oil is of little use.Heavy oils contain more nitrogen,sulfur and oxygen heterocyclic compounds,which can affect processing and product quality.Sulfur compounds can cause equipment corrosion and environmental pollution,nitrogen compounds can deactivate the catalyst or destroy the stability of the product,and the oxide will consume more hydrogen.Therefore,heavy oil cracking,desulfurization,denitrification and demetallization are the problems that all petroleum companies all over the world must face and need to overcome.An important factor in the upgrading of heavy oil is the choice of catalyst.Zeolite is a widely used porous catalyst material.Most of the zeolite catalysts currently used,such as ZSM-5 type,Y type and Beta,are microporous zeolites,and their pore size is relative to macromolecules in the petroleum industry.Too narrow,macromolecular reactants are difficult to transport efficiently in the catalyst pores.In order to overcome this difficulty,the researchers developed mesoporous zeolite catalysts,and subsequently successfully synthesized hierarchical porous materials,which greatly improved the transmission and reaction rate of macromolecules in the pores of catalysts.However,how to further improve the efficiency of heavy oil catalytic upgrading,improve product selectivity and reduce industrialization costs still face enormous challenges.In this thesis,the synthesis and functionalization of several hierarchical porous materials were studied with macromolecular catalysis.The n-hexadecane,1,3,5-triisopropylbenzene,tetrahydronaphthalene and dibenzothiophene were studied.Good results have been obtained for the macromolecular catalytic cracking,catalytic hydrogenation and catalytic desulfurization of probe molecules.In the experiment in Chapter 2,we used a ZSM-5 zeolite?Gel-ZSM-5?with a novel hierarchical porous hollow shell structure as a catalyst,and used n-hexadecane as a probe molecule to study the influence of the frameworks and acidity of the zeolites on macromolecular catalytic cracking reaction.The experimental results show that the mesoporous and macroporous structure in this novel catalyst is very beneficial to the rapid transport of macromolecular reactants,intermediates and cokings on the surface and inside,thus greatly improving the catalytic conversion rate and prolonging the catalyst life.In addition,a large number of acidic sites on the surface of the catalyst multistage pores can significantly improve the catalytic reaction performance for macromolecules and significantly improve the selectivity of the product.Especially in the short reaction time,this structure-activity relationship will be more significant.Therefore,reasonable acid distribution and hierarchical hollow thin-shell pore structure will give the catalyst better catalytic activity,selectivity and longer catalytic life in macromolecular catalytic cracking,which provides a favorable basis for designing new high-efficiency catalysts.In the experiment of the third chapter,we added the native zeolite in the synthesis process,with the alkali in the reaction system to alkali etch the native zeolite at a certain temperature for a certain time,and destroyed the whole structure of the zeolite to some extent to provide the seed crystal.Introducing CTAB as a template to hydrothermally synthesize a ANA zeolite with a micro-mesoporous composite.This zeolite is stacked on top of each other by a layered ANA zeolite having a high degree of crystallinity and interspersed into a highly dispersed spheroidal structure of 4-5?m.Through the study of the synthesis method,we speculate that the formation mechanism of this hierarchical structure may be that the native zeolite as a seed is destroyed by the alkali in the reaction system,forming a small ANA seed crystal or even a smaller silicon-aluminum ring.These seeds are uniformly dispersed around the micelles formed by CTAB to induce the ANA zeolite to grow along the micelle and reconstitute to form a highly crystalline sheet structure.Through various characterization methods,we know that the layers of this ANA zeolite are highly crystalline.The layer spacing is mainly concentrated at around 15 nm between 4 and 80 nm.It has strong surface acidity and thermal stability,higher catalytic cracking activity of 1,3,5-triisopropylbenzene,better product selectivity and longer catalytic life.In the experiment in Chapter 4,we studied the framework structures and microscopicity of three kinds of zeolites?traditional ZSM-5,micro-mesoporous composite shell ZSM-5 and house-of-cards-like ANA?after functionalized with metal Pt.Morphology and metal cluster morphology and loading sites,and the zeolite carrier type,reaction temperature and volume space velocity for tetrahydronaphthalene catalytic hydrogenation conversion and decalin selectivity were studied by using tetrahydronaphthalene as the probe molecule.influences.The catalyst with house-of-cards-like ANA zeolite as carrier has excellent catalytic activity for tetrahydronaphthalene and high selectivity to decalin due to abundant mesoporous macropores under low temperature and high space velocity reaction conditions.The empty shell type G-ZSM-5 has a high selectivity to small molecule products under high temperature and low space velocity reaction conditions due to its special thin-shell closed mesoporous structure.In the experiments in Chapter 5,we investigated the oxidative desulfurization?ODS?of dibenzothiophene?DBT?after functionalized with Ti on two hierarchical porous zeolites.The effects of catalyst carrier type,Ti dispersion,oxidant type,introduction of extractant and reaction time on the catalytic performance of the catalyst were investigated.Finally,it is concluded that the catalyst carrier has abundant and uniform mesoporous pores,which can promote the dispersion of Ti on the one hand,and also facilitate the transport of macromolecules on the other hand,thereby improving the catalytic performance of the catalyst.By introducing a polar extractant,not only can the conversion rate of DBT in the ODS process of H₂O₂ as an oxidant be greatly reduced,but also the removal of the product sulfone can be promoted to promote the depth of oxidative desulfurization.