Dual-Template Synthesis And Catalytic Performance Evaluation Of Two-Dimensional Layered Hierarchical Zeolite

Due to their ordered microporosity,superior catalytic activity,excellent thermal stability and hydrothermal stability,zeolites have been widely used in various heterogeneous catalysis processes.Normally,the conventional zeolites are bulky crystals in micon,resulting in very long diffusion lengths in micropores,which makes the conventional zeolites be less efficient or even inactive in the catalytic reaction with bulky substrates involved.Therefore,fabrication of zeolites with new-type pore systems in multilevel to improve the mass transfer resistance has become a considerable approach for the structure modification of zeolites,following with the creation of hierarchical zeolites.One of the most efficient methods to synthesize hierarchical zeolites is by using bifunctional structure-directing agents,in which the connection of the head groups of the multiple quaternary ammoniums to hydrophobic alkyl chains will simultaneously form zeolite frameworks and layered mesoporosity.However,the layered structure will collapse during the removal of the mesoscale micelles by calcination.In view of this,the duel-template synthesis of two-dimensional（2D）layered zeolites（ZSM-5and TS-1）with hierarchical layered mesoporosity was proposed and achieved with combined using the Bola-type surfactant(C_6-6-12（OH）₄)as the bifunctional structure-directing agent and tetrapropylammonium hydroxide（TPAOH）to stabilize the interlayered mesopores,and their catalytic performances were evaluated by the reactions of aromatic hydrocarbon alkylation and olefin epoxidation.1.Using C_12-6-6（OH）₄ as template to hydrothermally synthesize a series of two-dimensional layered hierarchical titanium-silicon zeolites LTS-1 with Si/Ti ratios of 25、50、75 and 100,and using XRD,The SEM,TEM,UV,IR and N₂ adsorption and desorption characteristics systematically characterize crystal morphology,pore structure,morphology,content and state of titanium,the results showed that LTS-1 was petal-like MFI type hierarchical zeolite,Most Ti atoms are tetrahedrally coordinated inside the silica framework.Using the 1-hexene and cyclooctene as the substrate macromolecules,systematically evaluate the selective catalytic oxidation performance of two-dimensional hierarchical titanium-silicon zeolites（LTS-1）,and comparing with the bulk titanium silicon zeolite CTS-1 and HTS-1 was guided with TPOAC.As the ratio of silicon to titanium increases,the reaction conversion first increases and then decreases.The catalytic performance of LTS-1₅0 is optimal.More Ti active sites on the surface of LTS-1₅0 are exposed,so catalytic performance is more excellent than HTS-1 and bulk CTS-1;Taking LTS-1₅0 as an example,reused experiments were carried out to show that the hierarchical titanium-silicon zeolites LTS-1 have good reusability.After fluorination treatment of LTS-1₅0,the surface of F-LTS-1₅0 after fluorination treatment is enhanced in hydrophobicity,and is more excellent in catalytic performance for epoxidation of macromolecular olefins.2.A series of two-dimensional layered hierarchical titanium-silicon zeolites with C_12-6-6（OH）₄/TPAOH molar ratios of 5/1,5/3,5/6 and 5/9 were synthesized using C_12-6-6（Br）₄/TPAOH dual template system,and were compared with DLTS-1₅/0 synthesized by using C_12-6-6（OH）₄.All are characterized by XRD,SEM,TEM,UV,IR and Ar adsorption and desorption,the structure,morphology,content and state of titanium were systematically characterized,as the amount of TPAOH added increased,the morphology,pore parameters and the existence state of the active sites were systematically regulated.Using the 1-hexene and cyclooctene as the substrate macromolecules,systematically evaluate the selective catalytic oxidation performance of two-dimensional hierarchical titanium-silicon zeolites（DLTS-1）.The hierarchical titanium-silicon zeolite synthesized by the dual template method have better catalytic performance than the zeolite synthesized by using C_12-6-6（OH）₄.And the DLTS-1₅/3with C_12-6-6（OH）₄/TPAOH molar ratio of 5/3 has the most excellent catalytic performance.3.A series of two-dimensional layered hierarchical silicon-aluminum zeolites with C_12-6-6Br₄/TPAOH molar ratios of 5/1,5/3,5/6 and 5/9 were synthesized by C_12-6-6Br₄/TPAOH dual template system,and were compared with LZ5-0 synthesized by using C_12-6-6Br₄.All are characterized by XRD,SEM,TEM,UV,IR,FTIR and N₂ adsorption and desorption,the structure,morphology,acid active sites were systematically characterized,the results showed that the morphology,pore parameters and acid active sites of hierarchical silicon-aluminum zeolites were systematically regulated after the addition of TPAOH.Using the catalytic conversion of benzyl alcohol in mesitylene,systematically evaluate the catalytic performance of hierarchical silicon-aluminum zeolites（LZ5）,comparing with the nanosheet LZ5-0 and the conventional catalyst CZ5,the samples synthesized by the dual template method displayed sufficiently higher conversion and selectivity.