Seed-assisted Syntheses Of SSZ-39 And High-silica GME Zeolites

Zeolites are a big family of crystalline microporous aluminosilicates,which are often used for ion exchange,adsorption and separation,and shape catalysis due to its uniform channel system.SSZ-39 is an aluminosilicate version of AEI type zeolite with excellent performance in NH3-SCR and MTO and thus its synthesis receives great attention.Up to now,the synthesis of SSZ-39 requires expensive piperidine-based organic template and high silica Y zeolite as a starting source(i.e.interzeolite conversion route).Recently,researchers have developed a seed-assisted synthesis method of SSZ-39,which is different to the interzeolite conversion.However,such route involves the utilization of large amount of organic template.Therefore,it is necessary to develop a novel and low-cost synthesis route for SSZ-39.GME zeolite was first discovered in nature and named as gmelinite.GME zeolite has a 12-membered ring channel parallel to the [001] direction and a two-dimensional intersected 8-membered ring channels perpendicular to the [001]direction.Before the identification of the topology structure of gmelinite,its special adsorption properties have been widely studied.However,the crystallinity of natural gmelinite is usually low and the chemical composition is relatively fixed.Most of the natural gmelinite has intergrowth with chabazite,making it is difficult to obtain pure phase and fault-free GME zeolite.Recently,researchers have developed a synthesis method of fault-free GME zeolite from interzeolite conversion using expensive Y zeolite as a starting source and piperidine-based organic template.But it is necessary to explore a new facile and economic synthesis route.In this thesis,we aim at creating a low-cost synthesis method for SSZ-39 zeolite and high silica fault-free GME zeolite.The main results are listed as follow:1.A seed-assisted hydrothermal synthesis route for SSZ-39 was developed with zeolite Y as a heterostructural seed,N,N-dimethyl-3,5-dimethylpiperidinium as OSDA,solid silica gel as silica source,and sodium aluminate as alumina source.The influence of Na OH/Si,OSDA/Si,Si/Al,and dosage of seed on the synthesis was systematically investigated.It was found that amorphous phase appeared if Na OH/Si is less than 0.337 and pure phase SSZ-39 could be obtained when Na OH/Si equals to 0.363,while a higher Na OH/Si would lead to a mixture of GME and AEI phase.The OSDA/Si in the initial reaction mixture is also a key factor.When OSDA/Si is as low as 0.130,FAU zeolite with low crystallinity is the sole product.Increasing the dosage of OSDA/Si to 0.190 will result in the pure phase of SSZ-39.At the condition of OSDA/Si between 0.145 and 0.175,a mixture of FAU and AEI phase will be obtained when Si/Al is as low as 16.13 and pure phase of SSZ-39 can be obtained when Si/Al=19.23.Besides,Seed is necessary in the synthesis since no crystalline product in the absence of seed,indicating a structuredirecting effect of seed,and pure phase SSZ-39 appeared with the quantity of seed reached 10.0 wt.% relative to the silica source.In this work,the synthesis condition is optimized,and the Si/Al of product is 8.57 and the crystallization process is studied via XRD and SEM.2.A seed-assisted hydrothermal synthesis route for SSZ-39 was developed with zeolite SAPO-18 as a seed,N,N-dimethyl-3,5-dimethylpiperidinium as OSDA,solid silica gel as silica source,and sodium aluminate as alumina source.The influence of Na OH/Si,OSDA/Si,and Si/Al on the synthesis was systematically investigated.It was found that amorphous phase appeared if the Na OH/Si is less than 0.384 and pure phase SSZ-39 could be obtained when Na OH/Si equals to 0.442,while a higher Na OH/Si would lead to a mixture of GME and AEI phase.The OSDA/Si in the initial reaction mixture is also a key factor.When OSDA/Si is as high as 0.175,a mixture of GME and AEI phase will be obtained and pure phase of SSZ-39 can be obtained when OSDA/Si between 0.145 to 0.159.The Si/Al in the initial reaction mixture is necessary in the synthesis since a mixture of GME and AEI phase was prepared when Si/Al less than 19.13 and pure phase of SSZ-39 cannot be obtained until Si/Al=19.13.In this work,the synthesis condition is optimized,and the Si/Al of product is 7.14 and the crystallization process is studied via XRD and SEM.3.A seed-assisted hydrothermal synthesis route for fault-free high silica GME was developed with zeolite Y as a heterostructural seed,N,N-dimethyl-3,5-dimethylpiperidinium as OSDA,solid silica gel as silica source,and sodium aluminate as alumina source.The Si/Al ratio of 6.8,determined by ICP,is much higher than that of CIT-9(Si/Al=3.5-4.0).The influence of Na OH/Si,OSDA/Si,Si/Al,and dosage of seed on the synthesis was systematically investigated.It was found that amorphous phase appeared if the Na OH/Si ratio less than 0.298 and a mixture of GME and AEI phase could be obtained when Na OH/Si is between 0.356 and 0.410.A pure phase of fault-free high silica GME zeolite will be obtained when Na OH/Si is between 0.470 and 0.552.A higher Na OH/Si ratio would lead to ANA phase.Seed is necessary in the synthesis since a mixture of ANA,GME and AEI phase was obtained in the absence of seed.A pure phase of GME will be obtained when OSDA/Si is between 0.130 and 0.190.In this work,the synthesis condition is optimized and the crystallization process is studied through XRD and SEM.