The Research On The Synthesis And Modification Of Beta Zeolites By Steam Assisted Conversion Method

The synthesis and modification of Beta zeolites have been studied in this dissertation,in which all samples are characterized by XRD、SEM、TEM、NH₃-TPD、FITR and XRF techniques.Esterification of levulinic acid is served as a probe reaction to evaluate the catalytic performance of the zeolites.Firstly,the synthesis of Beta zeolites via the steam-assisted conversion（SAC）method has been studied.The effect of TEAOH/SiO₂ on Beta zeolites synthesized by the SAC method and hydrothermal（HT）method has been investigated.The results showed that the lowest TEAOH/SiO₂ ratio was 0.06 for Beta zeolites synthesized by the SAC method,while it was 0.20 for the HT method.In addition,Beta zeolites with mesoporous structure aggregated by nano-crystals could be synthesized by the SAC method,but it could not be obtained by the HT method.Beta zeolites with SiO₂/Al₂O₃ratios between 5 and 30 have been synthesized by the SAC method and evaluated in the esterification of levulinic acid.It was found that the reactivity is enhanced with the increase of SiO₂/Al₂O₃ ratio and the sample with SiO₂/Al₂O₃=30 shows the highest TOF value at 15.3 h^-1.Secondly,the modification of Beta zeolites by introducing transtional metal species has been potimzed.Different transitional metals have been introduced into Beta zeolites by the impregnation method and in-situ SAC method,respectively.The results indicated that zeolites modified by in-situ SAC method showed a higher TOF value.Zeolites modified by Zr had the highest TOF value at 17.2 h^-1 comparing to other zeolites modified by W,Mo and Ti,which is 12%higher than that of bulk Beta zeolite.Lastly,the modification of Beta zeolite by introducing bimetallic speciecs has been carried out using the in-situ SAC method.W and Zr were loaded on Beta zeolites with different Zr precursors.The results turned out that catalyst modified by zirconium sulfate and ammonium tungstate showed higher reactivity,it was attributed to the formation of binary ZrO₂-WO₃ oxide acid.Comparing to Beta zeolites modified with different ZrO₂-WO₃ loadings,Beta zeolites loaded with 0.5wt%ZrO₂-WO₃ showed the highest TOF value at 19.1 h^-1,which is 25%higher than that of bulk Beta zeolite.