Magusin Pieter C M M, Zorin Vadim E, Aerts Alexander, Houssin Christophe J Y, Yakovlev Alexei L, Kirschhock Christine E A, Martens Johan A, van Santen Rutger A
Schuit Institute of Catalysis, Eindhoven University of Technology, The Netherlands.
J Phys Chem B. 2005 Dec 8;109(48):22767-74. doi: 10.1021/jp053217u.
Species at three stages in the self-assembly of zeolite ZSM-5 have been studied with one- and two-dimensional magic-angle-spinning 13C, 27Al, 29Si, and 1H NMR spectroscopy and compared with the earlier proposed structures: (1) precursor species containing 33-36 T sites around a tetrapropylammonium (TPA) cation, (2) nanoslabs consisting of a flat 4 x 3 array of such precursors, and (3) the final TPA-ZSM-5 zeolite. Synthesis was carried out in D2O to suppress the water and silanol protons. Under such conditions, the effective Si-H and Al-H distances measured with 29Si-{1H} and 27Al-{1H} rotational echo double resonance (REDOR) reflect the interactions between TPA cations and the surrounding aluminosilica. The 29Si-{1H} REDOR curves for Q4-type silicon atoms at the three mentioned stages are closely similar, as well as the observed 27Al-1H REDOR curve for the precursor species compared to that for the TPA-ZSM-5. This indicates that in addition to externally attached TPA, there is also internal TPA already incorporated at an early stage into the aluminosilicate in a similar way as in the final zeolite, in accordance with the earlier proposed MFI self-assembly pathway (Kirschhock et al. Angew. Chem. Int. Ed. 2001, 40, 2637). However, the effective distances extracted from the initial REDOR curvatures are significantly (10-15%) larger than those computed for the model. Since there is no temperature effect, we tentatively assign this difference to a reduction of the 29Si-1H and 27Al-1H interactions by multispin decoherence effects or self-decoupling caused by proton spin diffusion. By assuming the computed model distances and fitting Anderson-Weiss curves to the observed REDOR data, we obtain similar "decoherence times" in the order of 0.1 ms. The observed 29Si-{1H} REDOR dephasing for the Q3 sites in the precursors is significantly faster than that for the Q4 sites. This is tentatively ascribed to a partial deuteron-proton back exchange at the silanol positions.
利用一维和二维魔角旋转13C、27Al、29Si和1H核磁共振光谱对ZSM-5沸石自组装三个阶段的物种进行了研究，并与早期提出的结构进行了比较：(1) 围绕四丙基铵 (TPA) 阳离子含有33-36个T位点的前驱体物种，(2) 由这种前驱体的4×3平面阵列组成的纳米片，以及 (3) 最终的TPA-ZSM-5沸石。在D2O中进行合成以抑制水和硅醇质子。在这种条件下，用29Si-{1H}和27Al-{1H}旋转回波双共振 (REDOR) 测量的有效Si-H和Al-H距离反映了TPA阳离子与周围硅铝酸盐之间的相互作用。上述三个阶段Q4型硅原子的29Si-{1H} REDOR曲线非常相似，与TPA-ZSM-5相比，前驱体物种观察到的27Al-1H REDOR曲线也是如此。这表明，除了外部附着的TPA外，早期已经有内部TPA以与最终沸石类似的方式掺入硅铝酸盐中，这与早期提出的MFI自组装途径一致 (Kirschhock等人，《德国应用化学》，2001年，40卷，2637页)。然而，从初始REDOR曲率提取的有效距离比模型计算的有效距离大得多 (10-15%)。由于没有温度效应，我们初步将这种差异归因于多自旋退相干效应或质子自旋扩散引起的自去耦导致的29Si-1H和27Al-1H相互作用的降低。通过假设计算的模型距离并将安德森-魏斯曲线拟合到观察到的REDOR数据，我们获得了相似的 “退相干时间”，约为0.1 ms。前驱体中Q3位点观察到的29Si-{1H} REDOR去相位明显快于Q4位点。这初步归因于硅醇位置的部分氘-质子反向交换。
