丝光沸石水蒸气/酸浸渍脱铝的多核固体核磁共振研究

采用¹H,²⁹Si,²⁷Al魔角旋转固体核磁共振(MASNMR)及¹H-²⁹Si交叉极化(CP)技术研究丝光沸石水蒸气/酸浸渍脱铝过程中各种铝物质的结构与性质.结果表明,丝光沸石上骨架铝原子在水分子作用下,生成非骨架四配位铝物质[Al(OH)₃(H₂O)],分别在²⁷Al谱δ45和¹H谱δ3.0处出现共振信号,这种铝物质不同于扭曲四配位铝,在高温下进一步水合生成Al(OH)₃(H₂O)₂和Al(OH)₃(H₂O)₃,即非骨架五配位和六配位铝物质.¹H-²⁹SiCP和¹H谱证实,水蒸气脱铝使丝光沸石产生了大量的硅羟基和铝羟基.

A Multinuclear Solid State NMR Study on Dealumination of Mordenite by Steaming and Acid-leaching

The steamed and acid-leached mordenite samples were examined by high-resolution solid state 1H, 29Si, 27Al magic angle spinning (MAS) and 1H/ 29Si cross polarization (CP) NMR spectroscopic techniques in order to study the aluminum species and evaluate the dealumination process during steaming and leaching. The NMR experiments provide a direct evidence for the existence of nonframework four-coordinated Al species,Al(OH)3·H2O,giving rise to a 1H resonance at δ 3.0 and a 27Al shoulder peak at δ 45,which are different from the distorted four-coordinated Al species. At a high temperature,water molecules will favor the formation of these Al species and extra-framework penta- and hexa-coordinated Al species in the 27Al spectrum at δ 30 and δ 0,respectively. 1H/ 29Si CP and 1H MAS NMR showed the presence of an abundance of SiOH and AlOH groups in the dealuminated mordenites during the steaming process.