The distribution of Al on a zeolite framework can have a determining influence on chemical and catalytic properties. Those distributions are typically determined during synthesis as influenced by cationic organic structure directing agents (OSDAs). Here we use density functional theory (DFT) to compare the Al directing influence of N,N,N-trimethyl-1-adamantyl ammonium (TMAda⁺), an OSDA commonly used to crystallize CHA zeolite, with four isomers that retain the adamantyl structure but relocate the nitrogen center. Low energy configurations balance electrostatics-driven maximization of Al–Al and minimization of Al–N separations, the latter more important in OSDAs with more accessible charge centers. Statistical thermodynamics are used to predict thermal equilibrium Al distributions and corresponding Al pair features as a function of OSDA. All distributions differ from those predicted through naive application of Löwenstein’s rule, disfavor the placement of two Al second-nearest-neighbor or within a single six-ring, and introduce different biases toward eight-membered rings and more remote Al. Results illustrate the potential to influence Al location through OSDA selection.

中文翻译：

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有机结构导向剂对 CHA 分子筛中 Al 分布的预测影响


Al 在沸石框架上的分布会对化学和催化性能产生决定性影响。这些分布通常在合成过程中根据阳离子有机结构导向剂 （OSDA） 的影响来确定。在这里，我们使用密度泛函理论 （DFT） 来比较 N，N，N-三甲基-1-金刚烷基铵 （TMAda⁺）（一种通常用于结晶 CHA 沸石的 OSDA）与四种保留金刚烷基结构但重新定位氮中心的异构体的 Al 导向影响。低能量配置平衡了静电驱动的 Al-Al 最大化和 Al-N 分离的最小化，后者在具有更易接近电荷中心的 OSDA 中更为重要。统计热力学用于预测热平衡 Al 分布和相应的 Al 对特征作为 OSDA 的函数。所有分布都与通过天真应用 Löwenstein 规则预测的分布不同，不赞成放置两个 Al 第二近邻或单个六环内，并对八元环和更远的 Al 引入不同的偏差。