DETERMINATION OF THE QUADRUPOLE COUPLING-CONSTANT OF THE INVISIBLE ALUMINUM SPINS IN ZEOLITE HY WITH H-1/AL-27 TRAPDOR NMR
DETERMINATION OF THE QUADRUPOLE COUPLING-CONSTANT OF THE INVISIBLE ALUMINUM SPINS IN ZEOLITE HY WITH H-1/AL-27 TRAPDOR NMR
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DOI：
10.1021/ja00136a022
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发表时间：
1995-08-09
影响因子：
15
通讯作者：
VEGA, AJ
中科院分区：
文献类型：
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作者：
GREY, CP;VEGA, AJ
用双共振（TRAPDOR）NMR方法研究了HY沸石中质子酸中心H-1和Al-27核的布居转移。在实验中，H-1魔角自旋（MAS）回波信号的强度降低Al-27照射期间施加的回波序列的演变期间。A.提出了半定量理论来解释这些数据。作为辐射频率偏移的函数的信号减少的分析允许Al-27核的四极耦合常数的确定以及Al-H矢量的不对称参数和几何形状的估计。这项技术提供了一种手段，提取自旋相互作用参数的四极核，否则不可见的MAS NMR。该方法将NMR的能力扩展到表征催化感兴趣但通常不可见的铝原子，例如位于氧化铝载体表面和酸位点的铝原子。
The transfer of populations in double resonance (TRAPDOR) NMR method is applied to the H-1 and Al-27 nuclei of Bronsted acid sites in dehydrated zeolite HY. In the experiment, the intensity of a H-1 magic angle spinning (MAS) echo signal is reduced by Al-27 irradiation applied during the evolution period of the echo sequence. A. semiquantitative theory is proposed to explain the data. Analysis of the signal reduction as a function of the irradiation-frequency offset allows a determination of the quadrupole coupling constant of the Al-27 nuclei as well as an estimation of the asymmetry parameter and the geometry of the Al-H vector. This technique provides a means of extracting spin-interaction parameters of quadrupolar nuclei that are otherwise invisible by MAS NMR. The method extends the capabilities of NMR to the characterization of catalytically interesting, but typically invisible, aluminum atoms such as those located at the surfaces of alumina supports and at acid sites.