HY分子筛的脱铝过程的灵敏度增强27AlDQMASNMR研究.DOC

1、 HY分子筛的脱铝过程的 灵敏度增强 27Al DQ MAS NMR研究 喻志武 1, 郑安民 1, 王强 1, 陈雷 1, 徐君 1, Jean-Paul Amoureux2*, 邓风 1* (1.中国科学院武汉物理与数学研究所波谱与原子分子国家重点实验室，武汉磁共振中心，武汉 430071; 2.法国里尔科技大学，里尔， F-59652) 自从发现脱铝 沸石 分子筛的酸性 、 催化活性和选择性都比其相对应的未脱铝分子筛提高很多后，脱铝修饰一直以来都吸引了大量学者的关注 1。 脱铝过程中产生的非骨架铝对 其催化 性能的改善起 着至关重要的作用。然 而 关于脱铝分子筛中各种非骨架铝物种的详细结

2、构 、空间 邻近性和相互作用一直以来都没直接的实验证据， 这 极大 地妨碍 了 我们理解沸石 分子筛催化反应中其结构与性能的关系。 27Al 双量子 魔角旋转核磁共振（ DQ MAS NMR） 技术是研究固体材料中各种铝物种 空间 邻近性的 一种有力手段。 我们在高场下 (18.8 T)， 采用灵敏度增强的 27Al DQ MAS NMR技术 2研究了 HY分子筛脱铝过程中非骨架铝的详细演化 机理 。 图 1 显示的是不同 焙烧 温度脱铝 HY 分子筛的 27Al 单脉冲和双量子谱图 。 对于未脱铝HY分子 筛 (图 1a)，在其一维谱中只看到一个四配位骨架铝的信号 (61 ppm)，对应的二

3、维双量子谱图中只看到了 四配位骨架铝的自相关峰，表明骨架铝之间是彼此相互邻近 。当焙烧温度升高到 500 (图 1b)，产生了一个非骨架 六配位 铝的信号 (0 ppm)， 在相 应的二维谱出现一对交叉 峰，表明四配位和六配位 铝 之间是彼此 空间 邻近 的 。当温度继续升高到 600 (图1c)，产生了一个新的五配位非骨架铝的信号 (30 ppm)，在双量子谱图中 可以 看到三种不同铝物种之间彼此都存在交叉峰，说明这三种不同的铝物种之间 是 彼此 空间 邻近。 对于 700 脱铝的 HY 分子筛 (图 1d)，除了发现骨架四配位铝的信号发生了增宽之外，其谱图与 600 脱铝的谱图十分相似。通

4、过 27Al 三 量子技术，我们证实了存在一个新的非骨架铝四配位铝信号 (55 ppm)，在 相 应的双量子谱图中，可以看到其与五配位非骨架铝之间存在交叉峰 ，说明二者之间是彼此相 互 邻近的。另外，我们还可以看到 该非骨架铝四配位铝 与四配位骨架铝之间也 存在交叉峰 (55, 114)，这说明 它们也是空间 邻近的。 根据所得的实验和理论计算结果，我们提出了一个新的脱铝机理。 图 1 (a) HY, (b) HY-500, (c) HY-600, (d) HY-700分子筛的 27Al一维谱和双量子谱图，一维谱图画在各自对应的二维谱图之上。 Figure 1 27Al MAS and DQ

5、MAS NMR spectra of (a) parent HY, (b) HY-500, (c) HY-600 and (d) HY-700 zeolites. One-dimensional 27Al MAS spectra are plotted on top of the two-dimensional 27Al DQ MAS spectra. *通讯联系人 : 邓风：电话： 027-87198820, E-mail: ; Jean-Paul Amoureux: E-mail： jean-paul.amoureuxuniv-lille1.fr New Insights into the

6、 Dealumination of Zeolite HY Revealed by Sensitive-Enhanced 27Al DQ MAS NMR Spectroscopy at High Field YU Zhiwu1, ZHENG Anmin1, WANG Qiang1, CHEN Lei1, XU Jun1, AMOUREUX Jean-Paul2* , DENG Feng1* (1.State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Center for Magneti

7、c Resonance, Wuhan Institute of Physics and Mathematics, the Chinese Academy of Sciences, Wuhan 430071, China; 2.Lille Univ, UCCS, CNRS 8181, F-59652 Villeneuve Dascq, France) Since the discovery of the acidity, catalytic activity and selectivity of dealuminated zeolites are much higher than that of

8、 their respective parent samples, dealumination modification has received considerable attention.1 Extra-framework aluminum (EFAL) species generated during the dealumination process is crucial for the favorable influence on the catalytic properties of zeolites. However, the detailed structure of EFA

9、L species and the spatial proximities (or interactions) of various Al species in dealuminated zeolites were poorly understood. This strongly hamper the understanding of structure-property relationship in numerous zeolites that are widely used in petrochemical industry. In this work, we employed sens

10、itivity-enhanced 27Al DQ MAS NMR technique at high field (18.8 T) to study the evolution process of EFAL species of HY zeolite upon dealumination temperature. Figure 1 shows the 27Al MAS and 27Al DQ MAS NMR spectra of parent HY and HY zeolites calcined at different temperatures. For the parent HY, o

11、nly a signal at 61 ppm due to 4-coordinate framework Al is observable in the 27Al MAS NMR spectrum (Figure 1a). The signal exhibits a single auto-correlation peak in the 27Al DQ MAS NMR spectrum, indicating that these 4-coordinate framework Al species, which are associated with bridging hydroxyl gro

12、up (SiOHAl, Brnsted acid site), are in close proximity to one another. For the HY-500 zeolite, an additional peak at 0 ppm due to 6-coordinate EFAL appears in the 27Al MAS NMR spectrum (Figure 1b). Besides two auto-correlation peaks, one cross-peak pair at (61, 0) and (0, 61) ppm are observed in the

13、 27Al DQ MAS NMR spectrum (Figure 1b), corresponding to spatial proximity between 4-coordinate framework Al and 6-coordinate EFAL. For the HY-600 zeolite, a new signal at 30 ppm due to 5-coordinate EFAL is visible in the 27Al MAS spectrum (Figure 1c). Apart from three auto-correlation peaks, three d

14、istinct cross-peak pairs are present in the 27Al DQ MAS NMR spectrum of HY-600 (Figure 1c), indicating that the three different types of Al species are in close proximity to one another. For the HY-700 zeolite (Figure 1d), the existence of a new signal at ca. 55 ppm is confirmed by 27Al triple-quant

15、um MAS spectra, which can be assign to 4-coordinate EFAL species. Compared with the 27Al DQ MAS NMR spectrum of HY-600 zeolite (Figure 1c), a new strong cross-peak pair at (55, 87) and (32, 87) ppm are observed in this case, suggesting the spatial proximity between the 4-coordinate EFAL and the 5-co

16、ordinate EFAL species. In addition, a cross-peak at (55, 114) ppm is visible as well, corresponding to the spatial correlation between the 4-coordinate framework Al and the 4-coordinate EFAL species. Clearly, 27Al DQ MAS NMR experiment is capable of revealing the detailed spatial correlations among various aluminum species in HY zeolites with different extent of dealumination. References: 1 Corma A. Chem Rev, 1995, 95: 559. 2 Wang Q, Hu B, Lafon O, et al. J Magn Res, 2009, 200: 25.