Crystal structure, characterization and thermal stability of NH_4^+-exchanged -LIT-type zeolite
Crystal structure, characterization and thermal stability of NH_4^+-exchanged -LIT-type zeolite
复制标题
NH_4^-交换-LIT型沸石的晶体结构、表征及热稳定性
DOI：
10.1016/j.micromeso.2012.06.008
复制
发表时间：
2012
影响因子：
5.2
通讯作者：
池田拓史
中科院分区：
文献类型：
--
作者：
佐古渚;西原禎文;井上克也;吉田 司;池田拓史
我们研究了合成的LIT型沸石[Si8.74Al3.26O26H2K5.26]通过与氨的离子交换的晶体结构和热稳定性的变化。在NH 4+离子交换中，晶体结构发生了很大的变化，伴随着大的骨架变形。-LIT型沸石的晶体结构具有10个T位元环和abw型复合结构单元（CBU）。在这种拓扑结构中，骨架包含相邻硅烷醇基团之间的SiOH···OSi的氢键。钾离子以氢键形式存在于abw型CBU和赝配体中。NH_4 ~+处理的-LIT沸石（NH_4 LIT）的晶体结构为单斜晶系，空间群为P_（21/c），晶格常数为a=0.951nm，B=0.993nm，c=1.459nm，β=89.95°，属于准正交晶系。经处理的沸石的化学式估计为Si8.74Al3.26O22（OH）4·5.3（NH 4/H2O），其中NH 4/H2O比约为0.5。特征氢键消失，证实了由1H MAS NMR光谱。NH 4LIT分子筛在120°C时容易发生结构坍塌，而LIT分子筛的热稳定性超过700°C。合成的-LIT沸石的晶体结构和热稳定性发生了显着变化。NH 4+离子交换。离子交换后合成的LIT骨架结构中的氢键消失。
We investigated the change in the crystal structure and thermal stability of the synthetic –LIT type zeolite [Si8.74Al3.26O26H2K5.26] by ion exchange with ammonia. In the NH4+ion exchange, the crystal structure was considerably changed accompanied by a large framework deformation. The crystal structure of –LIT type zeolite has a 10 T-site membered ring and the abw-type composite building unit (CBU). In this topology, the framework comprises the hydrogen bond of SiOH···OSi between neighboring silanol groups. Potassium ions are included into the abw-type CBU and the pseudo micropore accompanied with hydrogen bonds. The crystal structure of the NH4+treated –LIT zeolite (NH4LIT) has a monoclinic symmetry with a space-group of P21/c, and lattice constants of a=0.951nm, b=0.993nm, c=1.459nm, and β=89.95°, which indicates a pseudo orthorhombic symmetry. The chemical formula of the treated zeolite was estimated to be Si8.74Al3.26O22(OH)4·5.3(NH4/H2O), where the NH4/H2O ratio was approximately 0.5. Characteristic hydrogen bonds disappeared, as confirmed by1H MAS NMR spectroscopy. The structural collapse of NH4LIT occurred easily by heating up to 120°C, whereas the thermal stability of the as-made –LIT zeolite reached over 700°C. BRIEF: Crystal structure and thermal stability of synthetic –LIT zeolite was dramatically changed via. NH4+ion exchange. Hydrogen bond in the framework structure of synthetic –LIT disappeared after ion exchange.