Study On The Synthesis, Characterization And Catalytic Activity Of Bi-Beta Zeolites

Bi-βzeolites (with BEA structure) were synthesized firstly by hydrothermal method used silica gel H as silica source, Bi(NO3)3·5H2O as metal source, sodium aluminate as aluminum source and tetraethylammonium hydroxide TEAOH (28%) as organic template. The nature characterization of the Bi-βzeolites were discussed based on the results of X-ray diffraction (XRD), nitrogen adsorption-desorption(BET), scanning electron microscopy(SEM), Fourier transform infrared spectroscopy (FT-IR), Ultraviolet-visible spectroscopy (UV-Vis) and thermogravimetric method(TG). It indicated that the synthesized samples had high crystallinity and bismuth was highly dispersed in the microstructure frameworks. The oxidation of styrene to benzaldehyde was investigated over the samples and the catalytic activity was high.The influence of the synthesize conditions on the crystallinity and catalytic activity of the molecular sieves had also been discussed. It was found that NaAlO2 concentration,template concentration,SiO2 concentration,crystallizing time and NaOH concentration would affect the synthesis of Bi-βzeolites. In the conditions as follows, SiO2/Al2O3=30,SiO2/Bi2O3=100, TEA+/SiO2=0.5, OH-/SiO2=0.1, crystallization temperature:145℃,crystallization time: 2d, the molecular sieve had the highest crystallinity and catalytic activities.Bi-βzeolites with different silica sources and different crystallization time were also synthesized. The samples were characterized by XRD and the catalytic activities were investigated used the oxidation of styrene to benzaldehyde as probe reaction. It indicated that the samples with different silica sources exhibited different catalytic activities. It was found the samples which used silica gel H, fumed silica and silica sol-NH3 as silica sources had higher catalytic activities than the samples with silica sol-Na and nano-SiO2 as silica sources, when the crystallization time was 2 days. When the time varied from 2 days to 4 days, all samples were in higher crystallinity and better activities, regardless of different silica sources.