摘要 研究經由(NH4)2SiF6 (AHFS)試劑處理Η−β沸石的27Al MAS NMR 和19F MAS NMR，並結合兩核種使用雙頻共振(double resonance)NMR 的技術，像19F{27Al} TRAPDOR 和27Al{19F} REDOR。在結果中顯示有加醋酸銨或沒加醋酸銨經由AHFS 試劑反應的的條件下，這兩種反應條件下的27Al MAS NMR 和19F MAS NMR 光譜有很大的不同，但是都會進行脫鋁反應，而脫鋁反應會影響骨架外的鋁之含量和狀態，並且會生成不同的鋁-氟化合物。 有加醋酸銨的情況下經由AHFS 處理Η−β沸石，在27Al MASNMR 上可觀測到四配位的鋁會脫離骨架而形成骨架外的鋁，而骨架外的鋁之化合物，測量19F MAS NMR 是相對應於化學位移-143ppm的吸收峰，是由(NH4)3AlF6 化合物所造成訊號。另一種處理方法是沒有加醋酸銨經由AHFS 處理Η−β沸石，可以在27Al MAS NMR 中觀測到化學位移於13ppm、0ppm 和一個很寬的化學位移由-20 到-90ppm，並觀測19F MAS NMR 光譜，發現除了有(NH4)3AlF6 的化合物生成，至少還有兩種不同的鋁-氟化合物產生。並且發現在AHFS 水溶液中形成的氟離子和pH 值有很大的關係。AHFS 和沸石反應時所產生的特徵峰，可利用27Al MAS NMR 和19F MAS NMR 光譜互相比較來說明可能形成的脫鋁機制。 The dealumination of zeolite H-b by ammonium hexafluorosilicate (i.e., (NH4)2SiF6, AHFS) treatment was investigated by 27Al and 19F magic angle spinning (MAS) NMR, combined with double resonance NMR. Our results demonstrated that the operating conditions of AHFS dealumination, that is, in the presence and absence of ammonium acetate (NH4Ac), strongly affect the amount, state, and nature of extraframework aluminum species (EFAl). Different aluminum fluoro-complexes after dealumination were detected. The correlation between 19F and 27Al spins was made with the use of double resonance methods such as 19F{27Al} TRAPDOR and 27Al{19F} REDOR NMR. There are significant differences in the 27Al and 19F NMR spectra of dealuminated H-b samples treated by AHFS with and without NH4Ac. For AHFS treated H-b in the presence of NH4Ac, 27Al MAS NMR revealed that tetrahedral aluminum at 54 ppm was mostly expelled from the zeolitic framework, resulting in the formation of two types of EFAl at 13 and 0 ppm. The EFAl at 0 ppm, corresponding to the 19F resonance at –143 ppm, can be assigned to (NH4)3AlF6. In the absence of NH4Ac, besides the EFAl species observed at 13 and 0 ppm, a new broad powder pattern spread from –20 to –90 ppm were observed. The 27Al NMR results demonstrated that at least two different forms of aluminum fluoro-complexes other than (NH4)3AlF6 were present after dealumination. These aluminum fluoro-complexes showed multiple lines located in the range of –150 to –158 ppm in the corresponding 19F spectra. It was found that the formation of fluorinated species after AHFS treatment strongly depends on the pH of the solution, i.e., in the presence and absence of NH4Ac. Complementary characterizations with 27Al and 19F NMR as a function of AHFS content are useful to make peak assignments, and to elucidate possible dealumination mechanisms.
