采用离子交换和焙烧等方法,对我国CXN天然沸石(STI型)进行改性.应用化学分析,粉末XRD,TG/DTA,^(27)Al MAS NMR,^(29)Si MAS NMR,低温N_2吸附等方法表征相关的结构、离子交换等性质.CXN沸石的晶胞组成Na_(0.2)Mg_(0.1)Ca_(8.4)[Al_(17.2)Si_(54.8)O_(144)]·65H_2O,属富钙型.经离子交换脱出Ca^(2+)后的沸石在焙烧过程中伴随有骨架脱铝,骨架的热稳定性已由原样的500℃以下提高到700℃以上.交换改性后的沸石,呈现反映该沸石微孔特性的Ⅰ型氮吸附等温线.
在TMEDA(四甲基乙基二胺)-Na_2O-SiO_2-Al_2O_3-H_2O体系(Ⅰ),Na_2O-K_2O-Al_2O_3-SiO_2-H_2-HCO_3^-CO_3^(2-) (Ⅱ)及Py(吡啶)-PrNH_2(正丙胺)-HF-SiO_2-H_2O体系(Ⅲ)中,分别合成了纯相FER沸石及FER硅沸石.用粉末XRD,FT-IR,^(29)Si MAS NMR及TG/DTA等表征其结构性质,并用超微量电子真空吸附天平测定这些沸石样品对正己烷,甲醇和水的吸附等温线.结果表明:各体系合成的样品虽然结晶度高,呈现出FER沸石的典型结构特征,但由于它们的组成和晶格微结构不同,热稳定性与吸附性质有明显的差异.在(Ⅰ)体系中合成的FER沸石层错缺陷少,晶格完美,正己烷与甲醇的吸附量可达到理论值,结构破坏温度为1190℃.红外精细谱及^(29)Si MAS NMR高分辨谱证明FER硅沸石具有十分完美的骨架结构.由于晶胞收缩,它对正己烷与甲醇吸附量略低于理论值,并呈现出高度的疏水性.它的结构破坏温度高于1300℃.在(Ⅱ)体系中合成的FER型沸石结构缺陷多,沸石孔中的钾离子不易被质子完全交换.它的正己烷与甲醇吸附量均较低,而水的吸附量相对较高.吸附现象表明,正己烷和甲醇都被吸附于FER沸石的十元环主孔道中,分压较高时,甲醇可通过八元环进入小笼,而水的吸附性质则主要与各样品的Si-OH缺陷及骨架中的阳离子含量有关.
The structures of silicalite-1 and H、 Na form of ZSM-5 with various SiO2/Al2O3 ratios were characterized by powder XRD, 29Si MAS NMR, and the desorption process of р-xylene (p-x) on the zeolites was investigated by using TG/DTG/DTA. SiOH defects of ZSM-5 have no relation with the content of structural Al. Silicalite-1 possesses perfect framwork structure without SiOH defects and structural Al. On a curve of TG/DTG/DTA, p-x adsorbed by silicalite completely desorbs in the range of 57-174℃by two steps, accompaned with endothermal effect. While on the TG/DTG/DTA curves of H, Na-ZSM-5, there is a third desorption step of p-x in the range of 180-600℃ with exothermic effect. Below 180℃ the number of desorbed p-x molecules is related to pore space, but over 180℃，it is related to SiOH and positive ion linking with the structural Al.
