| Zeolites are crystalline microporous aluminosilicates with unique pore systems and high thermal/hydrothermal stability,which are widely used as catalysts,adsorbents,and ion-exchangers.The continuous progress of zeolite science and technology is of great significance for the efficient utilization of petrochemical resources and the protection of atmospheric environment.The synthesis of zeolite Y（FAU zeolite with SiO2/Al2O3 ratio greater than 3.0）is of great significance for the petrochemical and refining industry.Ultra-stable Y（USY）zeolite is the core catalyst of fluid catalytic cracking,and its stability depends on the silica-alumina ratio.Zeolite Y with high SiO2/Al2O3 ratio has better stability,stronger Br?nsted acidity and higher catalytic cracking activity than normal zeolite Y.Steam dealumination is the mainstream technology for the preparation of ultra-stable Y.However,it will significantly reduce the crystallinity of ultra-stable Y and generate a large number of intracrystalline mesopores.Therefore,the direct synthesis of high-silica zeolite Y with high crystallinity is of great significance for the development of high-performance catalysts.At present,the highest SiO2/Al2O3 ratio of directly synthesized zeolite Y is 18.2 and further improving SiO2/Al2O3 ratio remains a great challenge.Pure silica zeolites have good hydrophobicity and are less affected by water vapor when adsorbing Volatile organic compounds（VOCs）,which has received extensive attention.However,the synthesis of pure silica zeolites usually requires a large amount of organic structure-directing agents and fluoride.Organic structure-directing agent can guide the synthesis of zeolites with specific structure,but its extensive use will lead to the increase of synthesis cost and pollutants in the treatment process.Fluoride has the effect of balancing the positive charge of organic structure-directing agents and directing the formation of composite building units（e.g.,double four-membered rings,d4rs）.However,protonated fluoride（i.e.,HF）are corrosive and excessive,which limits its large-scale industrial application due to pollution and safety issues.Fluoride ingested by the human body will affect the development of teeth and bones,and cause osteoporosis and multiple organ lesions.In recent years,with the increasingly stringent environmental protection policies and the need to reduce the cost of pure silica zeolites,it is of great significance to develop a green and economical synthesis method of pure silica zeolites.In addition,there are few reports on the synthesis of pure silica zeolite with d4rs in fluoride-free system.The development of synthetic methods for this kind of zeolite is urgent to be solved.In this thesis,tetrabutylammonium hydroxide（TBAOH）and tetramethylammonium hydroxide（TMAOH）were used as structure-directing agents（denoted as R in the recipe）,and high silica zeolite Y was used as seed to synthesized the high crystallinity zeolite Y with SiO2/Al2O3 ratio of more than 20 in one-step,which showed excellent performance in catalytic cracking reaction;by adding seed,which introduced composite building units into the synthesis system,and combining with the initial gel with low H2O/Si ratio,pure silica Beta,ITH,and CHA zeolites were synthesized under fluorine-free hydrothermal conditions.Among them,pure silica ITH zeolite was a zeolite with double four-membered rings synthesized under fluorine-free conditions;silicalite-1 with high crystallinity was synthesized by adding10 wt%seed under the R/Si ratio（0.01）of 76%lower than the theoretical R/Si ratio（0.042）.The main results of this thesis are as follows:1.Based on the synthesis strategy of dual structure-directing agent,zeolite Y with SiO2/Al2O3 ratio of 21.28 and 23.56 were synthesized by using high silica zeolite Y as seed,and the scale-up synthesis with 10 L autoclave for zeolite Y with SiO2/Al2O3 ratio of 21.28 was successfully conducted.The effects of various factors on the synthesis of high silica zeolite Y were systematically studied by exploring the recipe.The results show that:1)Zeolite Y with high SiO2/Al2O3 ratio can be synthesized by using organic structure-directing agent（TBAOH+TMAOH）with low charge density,reducing the use of inorganic cations（Na+）,and using zeolite Y with high SiO2/Al2O3 ratio as seed.2)The interaction between aluminum species and organic structure-directing agent during crystallization was observed by NMR.It shows that the organic structure-directing agent is decomposed in the zeolite pores.3)Zeolite Y with SiO2/Al2O3 ratio of 21.28 had excellent durability and activity in the catalytic cracking of isopropylbenzene,and the selectivity was still as high as 97.8%after 30 cycles.In the straight-run diesel catalytic cracking reaction,the yield of the target product liquefied petroleum gas was 36.45%,and the yield of propylene was10.32%.Compared with the commercial zeolite Y catalyst,the yield of the target product increased by nearly two percentage points.2.Three pure silica zeolites,Beta,ITH,and CHA,were hydrothermally synthesized under fluoride-free conditions with the assistance of seed.The effects of various factors on the synthesis of pure silica zeolites were systematically studied by exploring the recipe.The results show that:1)Pure silica Beta zeolite can be synthesized by controlling the Na/Si ratio of 0.03-0.05 and the H2O/Si ratio of 3-7;the crystallization time of pure silica Beta zeolite can be shortened to one day;under the same conditions,the adsorption capacity of pure silica Beta zeolite is 1.6 times higher than that of the one synthesized in the presence of fluoride ion.2)Pure silica ITH zeolite which has d4rs was synthesized under fluoride-free conditions.The addition of seed can introduce the composite building unit of ITH zeolite（i.e.,double four-membered rings,d4rs）into the synthesis system.3)Pure silica CHA zeolite can be synthesized under fluoride-free conditions by controlling the Na/Si ratio of 0-0.10and the H2O/Si ratio of 5 in the initial reaction mixture.3.Based on the economical and environmentally friendly synthesis concept,silicalite-1 zeolite with high crystallinity was synthesized by using seed.Through the exploration of the recipe,we obtained the following results:1)Without the introduction of seed,the silicalite-1 zeolite with a relative crystallinity of 100%（compared with the self-made standard sample）can be obtained only when the R/Si ration in the initial mixture is higher than the theoretical value of 0.042;2)In the adsorption of acetone and toluene,the silicalite-1 zeolite synthesized by adding 5 wt%seed from the initial mixture with a R/Si of 0.035 had higher pore adsorption than the normal silicalite-1 zeolite.3)The R/Si ratio in the synthesis of highly crystalline silicalite-1 zeolite can be decreased to 0.01 in the presence of 10 wt%seed. |
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