固態核磁共振於沸石 Y 經脫鋁及氟化後之鑑定與其機制探討;Solid State NMR Studies of Y zeolite Dealuminated with Ammonium Hexafluorosilicate

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/6208

Title:	固態核磁共振於沸石 Y 經脫鋁及氟化後之鑑定與其機制探討;Solid State NMR Studies of Y zeolite Dealuminated with Ammonium Hexafluorosilicate
Authors:	張白青;Pai-Ching Chang
Contributors:	化學研究所
Keywords:	脫鋁;六氟矽酸銨;dealumination;AHFS
Date:	2006-07-03
Issue Date:	2009-09-22 10:15:41 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	在本文中使用三種不同陽離子型態的 Y 沸石，以六氟矽酸銨((NH4)2SiF6, AHFS) 作為脫鋁反應試劑。並使用 27Al、19F、23Na 等多項核種的魔角旋轉核磁共振 (MAS NMR)，以及雙頻共振如 TRAPDOR、REDOR 等實驗作為主要研究技術。實驗結果證明在有無調整溶液 pH 值條件下，都會進行脫鋁反應，但在沸石結構的保存情況以及 MAS NMR的結果中有很大的不同。而脫鋁反應會影響骨架外的鋁的型態，而生成不同的氟鋁化合物。首先在 HY 沸石方面，在經過 AHFS 處理後，可在 27Al MAS NMR 觀察到四配位的鋁會脫離骨架而形成骨架外的六配位鋁化物，對應 19F MAS NMR 則位於 -141 ppm 乃是屬於 (NH4)3AlF6 化合物。在調整溶液 pH 值於 6-7 的情況下，所產生的主要產物為 (NH4)3AlF6 化合物，而在未經過調整溶液 pH 值的情況下，除了(NH4)3AlF6 之外還產生另外的結構，經過鑑定後確定為 NH4AlF4 化合物。其對應於 27Al MAS NMR 結果為位於 -20 ppm 至 -90 ppm的極寬之訊號，對應於 19F MAS NMR 則是觀察到兩個訊號峰，分別處於 -151 ppm 以及 -166 ppm. 而該訊號的產生需在 AHFS 反應劑量為 SiAHFS/AlHY >0.4。其次，在 NaY 沸石方面，在經過 AHFS 處理後，依然可在 27Al MAS NMR 觀察到四配位的鋁會脫離骨架而形成骨架外的六配位鋁化物。除了觀察到 (NH4)3AlF6 化合物之外，在不經過調整溶液 pH 值的情況下，在 19F MAS NMR 光譜上的主要訊號為位於 -190 ppm 屬於 Na3AlF6 化合物的訊號峰，以及一新的訊號峰位於 19F MAS NMR 中的 -158 ppm 位置。該訊號峰同時在有無經過調整溶液 pH 值的情況，尤其在調整溶液 pH 值於 6-7 的情況下，該產物訊號峰為 19F MAS NMR 上主要的訊號，經過雙頻共振技術確定其為 NaxAlFy 化合物。第三部分，在 NH4Y 沸石方面，經過 AHFS 處理後，可在 27Al MAS NMR 觀察到四配位的鋁會脫離骨架而形成骨架外的六配位鋁化物。在經過調整溶液 pH 值的情況下，即使在AHFS 反應劑量較高時，仍可在 XRD 繞射圖譜中觀察到其結構依然保持完好。在反應過後所產生的主要化合物為 (NH4)3AlF6。而在不經過調整溶液 pH 值的情況下，除了 (NH4)3AlF6 化合物之外，由 19F MAS NMR 觀察到產物中將包含較多種的 AlO6-xFx 化合物。 The dealumination of Y zeolites with different cations by ammonium hexafluorosilicate (i.e., (NH4)2SiF6, AHFS) treatment was investigated by 27Al and 19F magic angle spinning (MAS) NMR, combined with double resonance MAS NMR. Our results demonstrated that the operating conditions of AHFS dealumination, that is, with and without pH adjustment, strongly affect the amount, state, and nature of extraframework aluminum species (EFAl). Different aluminum fluoro-complexes after dealumination were detected. First, for AHFS treated HY with pH adjustment, XRD revealed that tetrahedral aluminum was expelled from the zeolitic framework, resulting in the formation of (NH4)3AlF6, which was evident from the peak at 0 ppm in the 27Al MAS NMR and at -141 ppm in the 19F MAS NMR. Without pH adjustment, we observed that the Y zeolite structure were progressively destroyed with increasing the amounts of AHFS. Besides (NH4)3AlF6, another phase structure was observed and identified as NH4AlF4 by XRD and MAS NMR. A new broad powder pattern spreads from -20 to -90 ppm (NH4AlF4) is observed at SiAHFS/AlHY > 0.40. The NH4AlF4 crystalline phase observed exhibited two 19F resonance peaks at -151 ppm and -166 ppm, which are assigned, for the first time, to the fluorine atoms in the terminal Al-F and bridging Al-F-Al groups, respectively. Secondly, for AHFS treated NaY with pH adjustment, MAS NMR revealed that tetrahedral aluminum was expelled from the zeolitic framework, resulting in the formation of Na3AlF6, which shows the characteristic peaks at -1.7 and -10 ppm in the 23Na MAS NMR and at -190 ppm in the 19F MAS NMR spectra. Without pH adjustment, the Y zeolite structure was again destroyed with increasing the amount of AHFS. A new NaxAlFy structure was observed with 19F MAS NMR for both treatments. Finally, for AHFS treated NH4Y with pH adjustment, XRD revealed that tetrahedral aluminum was expelled from the zeolitic framework and mainly formed (NH4)3AlF6. The Y zeolite structure was still retained even at a higher SiAHFS/AlHY ratio (~ 1.0) with pH adjustment. Without pH adjustment, on the other hand, the products of dealumination of NH4Y are various AlO6-xFx complexes.
Appears in Collections:	[Graduate Institute of Chemistry] Electronic Thesis & Dissertation

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