四乙基溴化铵-氟化物复合模板剂合成β沸石(Ⅱ)──β沸石晶化过程研究

Synthesis of β Zeolite Using Tetraethylammonium Brom ide Together with Fluoride as Composite of Template(Ⅱ) ── Studies on Crystallization Process of β Zeolite

采用 FT-IR,XRD,SEM,TG,ICP-AES等技术研究了四乙基溴化铵 ( TEABr) -氟化物复合模板剂体系合成 β沸石的晶化过程 .发现本体系 β沸石的合成遵循液相转变机理 ,在诱导期向生长期转变的转折点存在过渡态 ,氟离子对过渡态的形成和转变起到重要作用 .在诱导期初期固相是富铝的 ,但晶体生长期固相硅铝比基本不变 。

The crystallization process of β zeolite has been investigated by using FT IR, XRD, TG, SEM, and ICP AES. The samples were obtained by hydrothermal synthesis at 140 ℃ and chemical composition of the mixture used for synthesis can be expressed as n(Al 2O 3)∶n(SiO 2)∶n(TEABr)∶n(Na 2O)∶ n(NaF) ∶n(H 2O)∶n =1∶25∶7.5∶2.5∶3.75∶550∶6.25. The crystallization curve of zeolite β exhibits a typical S shaped characteristic. The typical framework IR absorptions at 567 and 518 cm -1 have different natures. The former is detected at the beginning of induction period and its intensity changes a little in induction period, but exhibits a direct correlation with crystallinity in growth period. The latter is not detected in the induction period, but exhibits the same trend in growth period. The large amorphous SiO 2 Al 2O 3 particles which are visible at the beginning of crystallization change into small grains during the induction period. n(SiO 2)/n(Al 2O 3) ratio of the solid phases obtained at different synthesis time changes significantly during the induction period, but changes a little in growth period. So the β zeolite crystal nucleus are formed via liquid phase synthesis mechanism. A typical gel in synthesis of β zeolite is transformed initially into a solid, which contains richer aluminium, minor F - and occluded TEA species. The aluminosilicate gel particles are dissolved by F - during the induction period and the transition complex, which has a specific weak X ray diffraction peak at 2θ=22.8° and specific DTG pattern, is formed at the turning point from induction period to growth period. During the growth period Si and Al transport from the liquid to the solid phase at almost the same rates. F - anion has greater influence on the formation and turning of transition complex.