Synthesis Of Zeolite From Laponite And Its Catalytic Properties In The MTO Reaction

Zeolites have been widely applied in the petrochemical field benefiting from their uniform molecular sized pores,excellent catalytic activity and great stability.To date,SAPO-34 with a CHA topological structure and ZSM-5 with an MFI topological structure have been widely used in the methanol to olefins(MTO)reaction.MTO process is the successful non-petrochemical route for the production of light olefins,which have been the research hotspot in the field of energy.The core technology lies in the research and development of zeolite catalysts,so the development of high-performance MTO catalysts and the green synthesis of zeolite catalysts are of great significance to the development of MTO field.Laponite has unique physical and chemical properties such as large surface area,many surface active sites and strong adsorption properties,which shows great potential in the synthesis of inorganic functional materials.Based on the physicochemical properties of laponite,a high-performance MTO zeolite catalyst was synthesized for the first time from laponite as a silicon source,and its crystallization process was investigated as well.The structure-property relationship between laponite and zeolite material was established,and the green synthesis of zeolite has been realized.In addition,the morphology of zeolite could be effectively controlled by adding biological macromolecular gelatin during crystallization.The details of results are as follows:(1)SAPO-34 zeolite with high catalytic activity was successfully synthesized by hydrothermal method from laponite as the single Si source,and its crystallization mechanism was investigated as well.The results show that the Si species depolymerized from laponite in the SAPO-34 zeolite are mostly exist in the state of Si(4A1).In addition,laponite itself contains Mg which could be introduced into the SAPO-34 zeolite during the crystallization process.This way was helpful for suppressing the metal species change into stable hydroxides in alkaline conditions,which effectively overcomes the inefficiencies of synthesizing metal-incorporated zeolite.Compared with the conventional SAPO-34 synthesized from TEOS,the catalytic life of SAPO-34 synthesized from laponite is increased by 64%,and the selectivity of light olefins is increased by about 11%,which can be attributed to the suitable strength of acidity.This work provides a new method for the synthesis of other metal-incorporated zeolite.(2)Mg-incorporated ZSM-5 zeolite exhibits spherical morphology composed of sheet-like crystals is synthesized directly from laponite and TEOS as Si sources via hydrothermal method,and the effect of the amount of laponite on the properties of zeolite was studied.The results show that the depolymerized laponite can not only be used as silicon source,but also can act as crystalline seeds and facilitate the ZSM-5zeolite nucleation.The existence of a large number of crystalline seeds is conducive to the formation of sheet-like elements,which can be formed sphere-like morphology through the self assembly.In comparison with ZSM-5(0)synthesized by using TEOS as single Si source,ZSM-5 zeolite synthesized from dual silicon sources exhibited better catalytic performance for MTO reaction.When the Si content of laponite in the total silicon source is 14%,the catalytic life of the synthesized ZSM-5 is increased by1.9 times,and the selectivity of light olefins is increased by 4.4%.(3)ZSM-5/SAPO-34 zeolite composites were successfully synthesized by adding ZSM-5 into SAPO-34 synthetic gel under hydrothermal synthesis conditions,and SAPO-34 as a part of the composite zeolite was synthesized from laponite as the Si source.The results show that the presence of ZSM-5 in the synthetic gel affects the nucleation and crystal growth rate.The gel network structure and unique charge properties of laponite in initial gel make it easy to adsorb on the surface of ZSM-5zeolite,which is conducive to the formation of a core-shell structured.These results reveal that the composite of ZSM-5 and SAPO-34 can not only form a hierarchical pore structure and abundant active centers,but also produce a synergistic effect on the composite phase interface,thus the catalytic life can be prolonged and the selectivity of light olefins can be improved.Compared with the T-ZSM-5/SAPO-34(2.5)zeolite composites synthesized from TEOS,the catalytic life of the ZSM-5/SAPO-34(2.5)composites synthesized from laponite is increased by 90%,and the selectivity of light olefins is increased by about 4.7%.(4)In order to synthesize zeolite more green and efficiently,nano ZSM-5 zeolite and small-sized SAPO-34 zeolite with excellent catalytic performance was successfully synthesized from laponite and TEOS as Si source together by dry gel conversion(DGC)method.For the synthesis of SAPO-34 zeolite,the SAPO-34 formed from laponite as the silicon source part can act as a seed crystal during the crystallization process to promote the nucleation of zeolite,which is beneficial to reduce the particle size of zeolite.For the synthesis of high-silicon ZSM-5 zeolite,the laponite not only can act as the Si sources for the zeolite synthesis but also exert“confined space”effect to control zeolite crystals growth.In addition,the Mg species from laponite can be incorporated into the framework of zeolite,which can moderate its acidity and thus shows excellent catalytic performance and reduce coke effectively during the MTO reaction.Thanks to the enhanced mass transport within the the reduction of crystals sizes and decreased acidity,the as-synthesized zeolite possesses excellent catalytic performance.This work provides a new idea for the synthesis of small grain zeolite.5 Based on the synthesis of ZSM-5 and SAPO-34 zeolite from laponite as the silicon source by DGC method,the synthesis of ZSM-5 and SAPO-34 zeolite was regulated by using biomolecular gelatin as an auxiliary template.The results show that ZSM-5 aggregates with b-axis orientation have been successfully synthesized by adding gelatin in the system.Gelatin can be easily adsorbed on(010)surface,which promotes the preferred growth of(010)crystal surface and inhibits the growth in b-axis direction.In addition,for the synthesis of SAPO-34 zeolite,gelatin interacts with the dry gel to limit the growth of crystals,preventing the high-degree intergrowth and aggregation of primary crystals.Finally,SAPO-34 zeolite with small grain accumulation structure was formed.Both b-axis oriented ZSM-5 zeolite and small grain SAPO-34 have excellent MTO catalytic properties.