Characterizing the First and Second 27Al Neighbors of Brønsted and Lewis Acid Protons in Zeolites and the Distribution of 27Al Quadrupolar Couplings by 1H{27Al} Offset REAPDOR
Characterizing the First and Second 27Al Neighbors of Brønsted and Lewis Acid Protons in Zeolites and the Distribution of 27Al Quadrupolar Couplings by 1H{27Al} Offset REAPDOR
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DOI：
10.1021/acs.jpcc.7b09544
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发表时间：
2017-11
影响因子：
3.7
通讯作者：
H. Koller;T. Uesbeck;M. Hansen;M. Hunger
中科院分区：
文献类型：
--
作者：
H. Koller;T. Uesbeck;M. Hansen;M. Hunger
应用~ 1H{27 Al}偏置旋转回波绝热通道双共振（REAPDOR）NMR实验，通过观察相邻~ 1H核间偶极耦合的影响，间接观察到酸性沸石H-β和H，Na-A中~（27）Al核的一级四极线形。该技术允许一个解决不同的铝环境的贡献，只要这些是由不同的四极加宽，反映不同的结构扭曲的特点。因此，通常显示大的四极耦合常数（CQ）的布朗斯台德酸位点可以与通常具有相当小的四极耦合的骨架外刘易斯位点区分开。1H{27 Al}偏移REAPDOR图案可以使用参考偏移REAPDOR曲线库（取决于四极耦合常数和不对称参数）采用高斯概率分布来模拟。CQ的单峰和双峰概率分布。
The application of 1H{27Al} offset rotational-echo adiabatic-passage double-resonance (REAPDOR) NMR experiments enables the indirect observation of the first-order quadrupolar lineshapes for 27Al nuclei in acidic zeolites H-beta and H,Na-A by observing the neighboring 1H nuclei under the influence of dipolar coupling between them. The technique allows one to resolve the contribution of different Al environments, provided that these are characterized by different quadrupolar broadenings, reflecting different structural distortions. Therefore, Bronsted acid sites that typically show large quadrupolar coupling constants (CQ) can be distinguished from extra-framework Lewis sites, which often have considerably smaller quadrupolar couplings. The 1H{27Al} offset REAPDOR patterns can be simulated employing a Gaussian probability distribution using a library of reference offset REAPDOR curves (depending on quadrupolar coupling constant and asymmetry parameter). Monomodal and bimodal probability distributions of CQ...