The Research On The Synthesis Of Sn-Beta Zeolite By Steam Assisted Conversion Method And Its Catalytic Performance For The Conversion Of Furfural

The synthesis of Sn-Beta Zeolite via steam assisted conversion method,hydrothermal crystallization method and isomorphous substitution method had been studied in this dissertation.The as-prepared zeolites have been characterized by the XRD,SEM,NH₃-TPD,XRF,FT-IR and Py-IR.The reaction of furfural and 2-butanol has been served as a probe to test the performance of Sn-Beta,Al-Beta and Sn-Al-Beta zeolites.Firstly,the factors that affect the synthesis of Sn-Beta zeolite by steam assisted conversion?SAC?method and hydrothermal crystallization method were investigated.It is shown that when the TEAOH/SiO₂ whose molar ratio is 4,the highest Sn content in the Sn-Beta zeolite synthesized by SAC method is 4.9 wt%?SnO₂?.When the TEAOH/SiO₂ whose molar ratio is greater than 4,it is impossible to obtain Sn-Beta zeolite by SAC method.For hydrothermal crystallization method,when the TEAOH/SiO₂ whose molar ratio is 3,the highest Sn content in the Sn-Beta zeolite synthesized by hydrothermal crystallization method is 3.6 wt%?SnO₂?.When the TEAOH/SiO₂ whose molar ratio is greater than 3,the yield of zeolite is extremely low.When the TEAOH/SiO₂ whose molar ratio is 0.1,neither Sn-Beta zeolite can be prepared.The hydrothermal crystallization method requires a higher OH^-/SiO₂ molar ratio than that of SAC method.To synthesize zeolites with high crystallinity,the OH^-/SiO₂ ratio required for the SAC method is 0.4,but a higher ratio at 0.6 is required for hydrothermal crystallization method.For the water content for composing gels as precursors of zeolites,it was found that the water content shows little effect on SAC method,but on the contrary,it is important for the hydrothermal crystallization method.When the H₂O/SiO₂ whose molar ratio is 7.8,Sn-Beta zeolite shows the the highest crystallinity.The most suitable crystallization temperature is 140?.However,the crystallization time for Sn-Beta formation is quite different.The SAC only needs 48hours,and the hydrothermal crystallization method requires 96 hours.Secondly,the synthesis of Beta zeolites via the isomorphous substitution method was studied.The results show that the first dealumination of Al-Beta zeolite with nitric acid does not substantially destroy the framework structure,and the highest tin content in the as-prepared samples is 3.1 wt%?SnO₂?.The Py-IR spectra were used to investigate the amounts of Bronsted acid and Lewis acid of the Sn-Al-Beta,Al-Beta and Sn-Beta.The results show that there is almost Lewis acid in the Sn-Beta zeolite with almost all weak acid.For Al-Beta zeolite,the amounts of Lewis acid and Bronsted acid are basically equal.But for the Sn-Al-Beta zeolite,the amount of Lewis acid is more than that of Bronsted acid,and almost all Lewis acid sites are weak acids.Lastly,the result of reactions between furfural and 2-butanol shows different reaction pathways over Sn-Beta and Sn-Al-Beta zeolite.For Sn-Beta zeolite,Lewis acid sites can reduce the aldehydes and ketones to alcohol,generating furfuryl alcohol.There are three types of reactions for the conversion of furfuryl alcohol:?1?The formation of?-angelica lactone under the catalysis of Bronsted acid sites,?2?The ring opening of furfuryl alcohol to produce levulinic acid under strong acid sites,and?3?The esterification of the resulting levulinate acid to 2-butyl levulinate.For the reaction over Al-Beta and Sn-Al-Beta zeolite,furfural produces?-angelica lactone under the catalytic action of acid sites.At a high temperature,?-angelica lactone is prone to isomerization changes.At the same time,a small amount of furfural can also be isomerized to?-angelica lactone over B and L acid sites.Both?-angelica lactone and?-angelica lactone can be ring-opened,and be isomerized to levulinic acid,or further alcoholysis to 2-butyl levulinate.The catalytic activity of Sn-Beta zeolite is related to the preparation method,Sn-Beta zeolite via hydrothermal crystallization method shows a TOF value at 3.4 h^-1,but via SAC,its TOF is 7.3 h^-1,which is higher than that of the former.