Synthesis Of Zeolites By Conversion Of Magadiite With Direction Of Seed Crystals

Zeolites are inorganic microporous materials composed of[SiO4]and[AlO4]-.Because of its good chemical stability,rich specific surface area and ordered pore structure,they have important applications in petroleum industry,ion exchange and adsorption,gas separation.The conventional synthesis method of zeolite is hydrothermal synthesis,and organic templates need to be added into the synthesis system to guide the formation of target zeolite.This synthesis method will cause a series of problems such as environmental pollution,waste of resources,increase of synthesis cost and so on,which does not meet the basic requirements of green chemistry.Therefore,seed crystals can be used as structure directing agents to direct the crystallization of zeolites,which can avoid environment problems brought by using organic templates.The synthesis of zeolite from layered silicate is widely used in scientific research and industrial production because of its high efficiency and high selectivity.Hence,the aim of this paper is to study the conversion of magadiite into zeolites with the direction of seeds,that is,to synthesize different types of zeolite in hydrothermal and solid-state systems by seed directed method without any organic template,and to investigate the changes of secondary building units and the role of seed.The main results are as follows:(1)Using magadiite as the raw material,zeolite beta has been prepared in hydrothermal and solid-state synthesis systems by seed directed method,respectively.The products were characterized in detail,and the effects of various factors on the synthesis results in the two systems were discussed and studied.It is found-that the five-membered rings(5Rs)and six membered rings(6Rs)of magadiite would be partially maintained in both two synthetic systems,and the seeds would be partially dissolved,which provided an active surface for the growth of the target zeolite.(2)Zeolite omega has been prepared in hydrothermal synthesis system and solid-state synthesis system by conversion of magadiite via seed directed method,respectively.The products were characterized in detail,and the effects of various experimental factors on the synthesis products were discussed.It is found that the seeds were only partially destroyed in hydrothermal system,while they almost destroyed in solvent-free solid-state system.During the transformation process,parts of the secondary building units of magadiite(5Rs and 6Rs)would be remained and participate in the growth of the framework of zeolite omega.(3)Chabazite has been synthesized in hydrothermal synthesis system and solid-state synthesis system by conversion of magadiite via seed directed method,respectively.The products were characterized systematically and effects of different experimental factors on the final products were studied.It is found that only 6Rs in magadiite would be retained in the two synthetic systems.While in the solid-state system,the seeds would be destroyed to a greater extent,resulting in producing more nuclei,so the final product presented irregular small spherical morphology;in the hydrothermal system,the seeds would be destroyed to a lesser extent,so chabazite grew along the surface of the seeds and finally presented popcorn morphology.(4)The morophology of products,yield and conversion time in different synthesis systems were compared and summarized.The differences of changes of secondary building units and seeds functions in hydrothermal synthesis and solid phase synthesis were studied,and conversion models were established.