Comparative Study On The Regularities And Properties Of Sn-Beta Zeolite Synthesized By Different Methods

This thesis focuses on the synthesis of Sn-Beta zeolite,especially the synthes via liquid phase isomorphic substitution,which is compared with Sn-Beta zeolite synthesized by the dry gel method and the hydrothermal synthesis method,respectively.XRD,SEM,TEM,Uv-Vis,FT-IR,Py-IR and NH3-TPD characterizations combining the esterification of levulinic acid and isomerization of glucose as probe reactions were used to study the catalytic performance of these as-prepared Sn-Beta zeolites.Firstly,with the Si O2/Al2O3=38 Beta zeolite（Al-Beta）,Sn-Beta was prepared by aluminum dealumination and tin supplement:dealumining framework Al by acid treatment to obtain silicious zeolite precursor with a ratio of Si O2 to Al2O3 at 1053（Deal-Al-Beta）.Isomorphous substitution of Sn was realized by adding tetraethylammonium hydroxide（TEAOH）as templating agent,tin salt and solvent under the hydrothermal synthesis condition.The effects of tin source and,content,and the amount of template on the synthesis of Sn-Beta zeolite（IS-Sn-Beta）were investigated,respectively.The optimized synthetic conditions for IS-Sn-Beta zeolite were realized,in which Sn Cl4·5H2O as tin source,0.1 M tetraethylammonium hydroxide（TEAOH）,a weight ratio of template to Deal-Al-Beta zeolite at 3,6 wt%of Sn addition,and 24 h crystallization at 140 ^oC were used.Secondly,without the aid of the minerizer containing F^-,Sn-Beta zeolite was prepared by the dry-gel conversion method and hydrothermal synthesis method respectively,which were denoted as,DG-Sn-Beta and HT-Sn-Beta.DG-Sn-Beta zeolite shows spindle-shape,and HT-Sn-Beta zeolite shows thick square with larger partice size.However,DG-Sn-Beta exhibits a higher crystallinity.Compared with isomorphous substitution method,both dry-gel conversion method and hydrothermal synthesis method require more amount of template,longer crystallization time,and extremely lower product yield.Therefore,the seeds were used in the dry-gel conversion method and hydrothermal synthesis method to promote crystallization,respectively,in which DG-Sn-Beta-SC and HT-Sn-Beta-SC zeolites were obtained.DG-Sn-Beta-SC shows as square sheet with～200 nm,while HT-Sn-Beta-SC zeolite exhibits micro-spherical morphology.XRF and FT-IR characterization of DG-Sn-Beta,HT-Sn-Beta,DG-Sn-Beta-SC,HT-Sn-Beta-SC and IS-Sn-Beta zeolites were carried out.IS-Sn-Beta zeolite has a high Sn content of 2.15%,as well as obvious characteristic peaks crrespondingt to the framework Sn species in FT-IR spectra.The esterification of levulinic acid as a probe was used to test the catalytic activity of as-prepared Sn-Beta zeolites.IS-Sn-Beta possesses the highest TOF value of 4.3 h^-1.In order to test the L acid catalytic performance of Sn-Beta zeolite,glucose isomerization to fructose was used to compare the activity of Sn-Beta zeolites prepared by the isomorphous substitution method,the dry-gel conversion method and the hydrothermal synthesis method.IS-Sn-Beta zeolite also shows the highest TOF value at7.2 h^-1.