CXN天然沸石的研究 VI. 耐酸性及不同阳离子型沸石结构的热稳定性

以X射线粉末衍射(XRD)结晶度测定法观测CXN (STI型)天然沸石在不同浓度盐酸(HCl)热溶液中的结构耐酸性, 以及比较和研究用不同方法制备的结构超稳化高硅H-STI-I和H-STI-II沸石及其不同阳离子交换型M-STI (M＝Li, Na, K, Ca, Ag) 系列沸石在程序阶梯升温过程中的结构热稳定性. 用X射线荧光散射(XRF), ²⁹Si与²⁷Al固体核磁共振(MAS NMR)表征超稳化高硅H型沸石的组成与结构性质. 结果表明该天然沸石在浓度低于2 mol/L盐酸中可较长时间保持结构完美. 视阳离子类型不同, 经1173 K焙烧后M-STI-I系列沸石与M-STI-II系列沸石相对结晶度降低百分数分别为2.5%～18% 与0～35%. 在M-STI-I系列沸石中, 焙烧前后相对结晶度下降幅度的次序为K型＜(H, Li, Na)型＜(Ca, Ag)型, 而M-STI-II系列沸石, (Na, K)型＜(Li, H, Ca)型＜Ag型. 从沸石骨架硅铝比、结构缺陷、阳离子种类及其氧化物形成热等方面讨论影响沸石结构热稳定性的因素.

Studies on CXN Natural Zeolite VI. Acid-resistant Property and Thermal Stability of Various Cation Forms

The acid-resistant property of natural CXN zeolite (type STI) in the hot HCl solution with various concentrations, and the thermal stability of ultra-stable high-silica H-STI-I and H-STI-II zeolites prepared by different procedures, and various cation forms of M-STI-I series and M-STI-II series (M＝Li, Na, K, Ca, Ag) zeolites under the stage-temperature programmed calcinations were investigated with measuring the crystallinity by powder X-ray diffraction (XRD). The composition and the structure properties of H-STI-I and H-STI-II zeolites were characterized with X-ray fluorescence scattering (XRF), ²⁹Si and ²⁷Al MAS NMR. The results suggest that the crystal structure of the natural zeolite remained relatively perfect in hot HCl solution with the concentration lower than 2 mol/L in a long period. Dependent on the species of the cations in the zeolites, the relative crystallinity of M-STI-I series and M-STI-II series zeolites was decreased 2.5%～18% and 0～35% after calcination at 1173 K, respectively. The decrease of the relative crystallinity was in the order of K＜(H, Li, Na)＜(Ca, Ag) form for M-STI-I series zeolites, and in the order of (Na, K)＜(Ca, H, Li)＜Ag form for M-STI-II series ones, respectively. Several factors affecting the thermal stability of the zeolties, such as the framework Si/Al ratio, structural defects, cation forms, and the formation heat of the relative oxides were discussed.