Study On The Synthesis And Modification Of FER Zeolites For Isomerization Of N-butene

In this dissertation,a series of FER zeolites were synthesized using different organic amines as templates.The effects of templates on the pore structure,morphology,acidity,grain size of the synthesized FER zeolites and their catalytic properties for isomerization of n-butene were systematically investigated.The modified FER zeolites with higher activity and stability were successfully prepared by exploring the conditions of steam modification of the synthesized FER molecul ar sieves.On this basis,X-ray diffraction(XRD),Micro-mesoporous full static adsorption(BET),Ammonia programmed temperature desorption(NH3-TPD),Pyridine adsorption(Py-IR),Solid nuclear magnetism(NMR),Scanning electron microscopy(SEM),Thermogravimetry(TG),High resolution transmission electron microscopy(HRTEM)were used to characterize the acidity,pore structure,morphology and atomic coordination envirornment of FER molecular sieves.The relationship between structure and catalytic performance of FER zeolites in isomerization of n-butene was discussed.The main results are as follows:(1)In exploring the effects of EDA,Py and CHA templates on the synthesized FER molecular sieves,it showed that Py-FER zeolite had the best isomerization activity and catalytic stability of n-butene at a space velocity of 8 h-1.The yield of isobutene could reach 37%and be stable for more than 20 hours;the yield of isobutene of EDA-FER zeolite was only 32%,and the catalytic stability can hardly be maintained.The yield of isobutene in CHA-FER zeolite was up to 35%,and it maintained high yield and catalytic stability in a short time(?1Oh).(2)The acidic characterization results of NH3-TPD and Py-IR show that the acidity of EDA-FER zeolite and Py-FER zeolite are basically the same,and both are weaker than that of CHA-FER zeolite.Quantitative analysis showed that the weak acid content of FER zeolites synthesized by these three templates was very close,but the medium strength B acid sites of Py-FER zeolite were much more.SEM and BET characterization showed that Py-FER zeolite had a layered structure with smaller grains and more abundant mesoporous compared with EDA-FER and CHA-FER zeolites.Such acidity and structural characteristics determine that Py-FER not only maintains high activity,but also has good reaction and diffusion performance,which can maintain better catalytic stability.(3)In order to further improve the catalytic performance and stability of FER molecular sieves,steam modification was used to treat FER molecular sieves.The results show that the pore structure and acidity of FER zeolite can be effectively adjusted by steam treatment,and the catalytic activity and stability can be improved simultaneously.FER zeolite had the best catalytic performance after 30mim treatment at 1.0 mL/min and 370 °C,respectively.Relevant characterization results showed that the structure of micropore and mesoporous could be controlled simultaneously by higher steam treatment temperature(370-420 °C)and larger steam flow rate(1-3 mL/min).On the other hand,the proper matching of mesoporous and microporous materials plays a major role in the stability of FER catalysts,while acidity changes play a minor role.In a word,pore structure,acid property,grain size,Si-Al coordination environment and other factors affect the catalytic performance of FER zeolite.In essence,it can be summarized as improving the connectivity of micropores and mesopores to expose more acid centers and achieve high catalytic activity while maintaining high stability.