Preparation,Characterization Of Supported Noble-metal SSZ-13 And Their Catalytic Performance In Ring Opening Of Naphthenic Compounds And Hydrogenation Of Naphthalene

Ring opening?RO?of naphthenic molecules and hydrogenation of aromatic compounds are important reactions for improving the quality of diesel oil.Cracking reaction is often accompanied by ring opening of naphthenic molecules.While in the process of aromatics hydrogenation,the noble metals are easily poisoned by sulfur compounds.Therefore,in order to solve the above problems,it is necessary to develop efficient catalysts to enhance the activity and sulfur resistance of the catalysts.SSZ-13 is a small pore zeolite.The unique framework structure and acidicity have made it useful as support and catalyst in the removal of NOx and the conversion of methanol to olefin.SSZ-13 zeolite has also been used for gas separation and adsorption.However,the works on the ring opening and hydrogenation of aromatic compounds have been rarely reported.Based on the structural characteristics and acidicity of the SSZ-13,in this thesis,the effects of supported methods of noble metal on SSZ-13,surface properties and crystal sizes of SSZ-13 supports on the physical properties and catalytic performances of the prepared supported catalysts were systematically studied.The main results are as follows.1)Synthesis and characterization of SSZ-13 zeolitesA series of SSZ-13 zeolites were synthesized in the hydrothermal system.The effects of crystallization conditions?crystallization temperature,crystallization time?and the incient gel composition?silica-alumina ratio,alkalinity?on the synthesis of SSZ-13 zeolites were investigated and the synthesis parameters were optimized.The core-shell zeolite SSZ-13@Nano SSZ-13 samples were successfully synthesized by secondary synthesis.2)Praparation,characterization and catalytic performance of Ir/HSSZ-13Ir/HSSZ-13 catalysts were prepared by impregnation method and their catalytic performance was investigated in methylcyclopetane?MCP?ring opening.The results of TEM,NH₃-TPD and MCP ring-opening reaction indicated the supported Ir species were mainly located on the external area of SSZ-13 supportes.Although the small pore of SSZ-13 support can prevent the MCP from accessing to its cages,the prepared Ir/HSSZ-13 exhibited excellent catalytic performance on MCP RO reaction under the interaction between the small aount of acid sites on the external surface of SSZ-13.In addition,the influences of reaction factors such as reaction pressure,reaction temperature,time and crystal sizes of the SSZ-13 supports on the catalytic performance over Ir/HSSZ-13 were investigated.3)Preparation,characterization and catalytic properities of Pt/HSSZ-13with Pt in different locations?)Catalyst design:The main aim in this thesis is to prepare the catalysts with high sulfur-resistance as well as high catalytic activity for polycyclic aromatic hydrocarbon.For realizing the above aim,a novel catalyst design route was proposed in this thesis.The route involves encapsulation of noble-metal species in SSZ-13 cages.The small pore size of SSZ-13 can effectively prevent the organic sulfur compounds from accessing the encapsulated Pt species,while the small H₂ molecules can readily diffuse into the cages of SSZ-13 and dissociate on the encapsulated Pt species.The dissociated hydrogen species,transported from the pore to the external surface of SSZ-13 via–OH groups and react with naphthalene adsorbed on the external surface of SSZ-13.?)Preparation and characterization:A series of Pt/HSSZ-13 catalysts were prepared by different methods:1)In situ encapsulation of Pt NPs within SSZ-13?Pt/HSSZ-13?Is??was realized during zeolite crystallization using bifunctional?3-mercaptopropyl?-trimethoxysilane ligands.The results of TEM and styrene hydrogenation show that Pt species are successfully encapsulated in SSZ-13 cages;2)The Pt species were also encapsulated in SSZ-13 with the different Si/Al ratios by impregnation,calcinations and reduction?Pt/HSSZ-13?Im??.In this preparing process,the calcination temperature has a great influence on the locations of Pt species.Upon calcination at 350?,the Pt species in Pt/HSSZ-13?Im?-350 did not uniformly distributed in the SSZ-13 crystal,but mainly located in the cages on the periphery of SSZ-13 crystals.In contrast,upon calcined at 550?,the Pt species in Pt/HSSZ-13?Im?-550 were uniformly distributed on the SSZ-13crystal like Pt/HSSZ-13?Is?.3)The Pt species located on the external surface of HSSZ-13?Pt/HSSZ-13?Ex??were prepared by loading Pt colloidal suspension on the surface of HSSZ-13.?)Catalytic properties:Pt loading methods greatly influences the catalytic performance of the prepared catalysts.Even if the three catalysts,Pt/HSSZ-13?Im?-350,Pt/HSSZ-13?Is?and Pt/HSSZ-13?Ex?have the same Pt content,they showed different catalytic performance in naphthalene hydrogenation.The differences closely related to the locations of Pt species in SSZ-13.For Pt/HSSZ-13?Ex?,the supported Pt species were mainly located on the external surface of SSZ-13,and the Pt species are accessible to naphthalene.Whereas most of the Pt species are located in the cages of SSZ-13 in Pt/HSSZ-13?Im?-350 and Pt/HSSZ-13?Is?as evidenced by CO adsorption and TEM results,Pt species in the two catalysts were inaccessible to naphthalene due to the larger size of naphthalene larger than the pore size of SSZ-13.Therefore,the significant naphthalene conversions obtained over Pt/HSSZ-13?Im?-350 and Pt/HSSZ-13?Is?involve spillover activated hydrogen atoms.In this process,small H₂ molecules can readily diffuse into the cages of SSZ-13 and dissociate on the encapsulated Pt species.The dissociated hydrogen species,transported from the pore to the external surface of SSZ-13 and react with naphthalene adsorbed on the external surface of SSZ-13.So Pt/HSSZ-13?Im?-350 has higher hydrogenation capacity and excellent sulfur resistance in the test of sulfur resistance.Compared with other support supported Pt catalysts,Pt/HSSZ-13?Im?-350 also has obvious deep hydrogenation ability and sulfur resistance.