Designed Synthesis Of MFI Zeolites From Sustainable Routes

Petrochemical industry is the lifeblood of the country and more than 90 percentage of the reactions requires the participation of catalysts,which is an important guarantee for the industry to maintain economic development with high quality.Among them,MFI zeolite plays a critical role in catalytic crackings,methanol to olefins,and isomerizations.Generally,MFI zeolite is synthesized under hydrothermal conditions in the presence of organic structure directing agents(OSDAs)such as quaternary ammonium cations and organic amines.However,the costly OSDAs lead to the increase of production cost,and the removal of these OSDAs by calcination is easy to produce harmful gases.Recent works show that the seed-direct method can avoid the use of OSDAs,but the Si/Al ratios of MFI zeolites is limited,which cannot meet the requirements of catalytic reactions such as methanol to olefins.In order to achieve the goal to develop a more green,economic and sustainable zeolite synthesis route to meet the needs of industrial catalysis,it is focused on design of new sustainable routes for synthesis of MFI zeolites.In chapter two,it is shown the synthesis of high silicon ZSM-5(MFI topology)zeolite with ethanol as additive under in the absence of OSDAs and solvent,where the Si/Al ratios of the zeolite products could be adjusted in the range of 35～230.The key to this success is to use the aluminosilicate precursors with four-coordinated aluminum species as raw materials and the ethanol in the final product could be removed by washing without calcination In addition,this method can be extended to introduce heteroatoms in the zeolite framework such as Fe-ZSM-5,B-ZSM-5,and Ti-ZSM-5 and synthesis of other zeolite structures such as of TON,MTT and*MRE.Furthermore,the high silicon ZSM-5 zeolite obtained by this method has similar propylene selectivity and lifetime in methanol to propylene(MTP)with the zeolite synthesized with OSDAs.In chapter three,it is shown a route for one-pot synthesis of full-crystalline shaped zeolites without solvent and OSDAs,where the whole process avoids the use of OSDAs and calcination for template removal.The obtained zeolites have good mechanical strength and excellent catalytic performances in MTP.In contrast,the traditional synthesis of full-crystalline shaped zeolite requires to use OSDAs for secondary crystallization to convert the inorganic binder into the target zeolites,where the use of OSDAs and calcination for template removal is necessary.This sustainable one-pot synthesis route may provide a new research idea for the preparation of shaped zeolites.In chapter four,it is shown a solvent-free and OSDAs-free route for synthesis of core-shell structure MFI zeolite(ZSM-5@Silicalite-1).Compared with ZSM-5 zeolite without silicalite-1 shell,the core-shell ZSM-5@silicalite-1 zeolite catalyst significantly improves the selectivity of p-xylene and catalyst life in the alkylation of methanol-toluene.In addition,the solvent-free synthesis in this chapter completely avoids the dissolution of ZSM-5 zeolite,which offers a new opportunity for preparing composite zeolite structures in the future.In chapter five,it is shown the synthesis of ZSM-5 zeolite using ethylenediamine as OSDAs without sodium cations,which simplifies the preparation of H-type ZSM-5zeolite by ion exchange and calcination.Very importantly,most ethylenediamine in zeolites can be removed by high temperature vacuum treatment,giving ZSM-5 zeolite with micropore volume of 0.13 cm~3/g,which significantly reduces the NO_x emission.In addition,the mother liquor for synthesis of zeolites can be reused,which is environmentally friendly for zeolite synthesis.