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The acidic nature of "NMR-invisible" tri-coordinated framework aluminum species in zeolites.
Chemical Science ( IF 7.6 ) Pub Date : 2019-09-12 , DOI: 10.1039/c9sc02634g Shaohui Xin 1, 2 , Qiang Wang 1 , Jun Xu 1 , Yueying Chu 1 , Pengfei Wang 3 , Ningdong Feng 1 , Guodong Qi 1 , Julien Trébosc 4 , Olivier Lafon 4, 5 , Weibin Fan 3 , Feng Deng 1
Chemical Science ( IF 7.6 ) Pub Date : 2019-09-12 , DOI: 10.1039/c9sc02634g Shaohui Xin 1, 2 , Qiang Wang 1 , Jun Xu 1 , Yueying Chu 1 , Pengfei Wang 3 , Ningdong Feng 1 , Guodong Qi 1 , Julien Trébosc 4 , Olivier Lafon 4, 5 , Weibin Fan 3 , Feng Deng 1
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The unambiguous characterization of different acid sites in zeolites is of great importance for understanding their catalytic performance and the rational design of highly efficient zeolite catalysts. In addition to various well-characterized extra-framework Al species, a tri-coordinated framework aluminum species can also serve as a Lewis acid site in zeolites, which is "NMR-invisible" owing to its extremely distorted local environment. Here we provide a feasible and reliable approach to elucidate the acidic nature of the tri-coordinated framework Al in dehydrated H-ZSM-5 zeolites via sensitivity-enhanced two-dimensional (2D) multiple nuclear correlation NMR experiments coupled with trimethylphosphine oxide (TMPO) probe molecules. Two types of tri-coordinated framework Al sites have been unambiguously identified, which amount to 11.6% of the total Brønsted and Lewis acid sites. Furthermore, it was found that synergistic effects arising from the close spatial proximity between the tri-coordinated framework Al site and the Brønsted acid site lead to the generation of superacidity (with an acid strength stronger than 100% H2SO4) in the zeolite.
中文翻译：
沸石中“核磁共振不可见”三配位骨架铝物质的酸性。
沸石中不同酸位点的明确表征对于理解它们的催化性能和高效沸石催化剂的合理设计具有重要意义。除了各种特征良好的外骨架铝物种外，三配位骨架铝物种还可以作为沸石中的路易斯酸位点，由于其极度扭曲的局部环境而“核磁共振不可见”。在这里，我们提供了一种可行且可靠的方法，通过灵敏度增强的二维 (2D) 多核相关 NMR 实验结合三甲基氧化膦 (TMPO) 来阐明脱水 H-ZSM-5 沸石中三配位骨架 Al 的酸性性质探针分子。已明确识别出两种类型的三配位骨架 Al 位点，共 11 个。Brønsted 和 Lewis 酸位点总数的 6%。此外，发现由三配位骨架 Al 位点和 Brønsted 酸位点之间的紧密空间接近产生的协同效应导致沸石中产生超酸性（酸强度高于 100% H2SO4）。
更新日期：2019-11-07
中文翻译：
沸石中“核磁共振不可见”三配位骨架铝物质的酸性。
沸石中不同酸位点的明确表征对于理解它们的催化性能和高效沸石催化剂的合理设计具有重要意义。除了各种特征良好的外骨架铝物种外，三配位骨架铝物种还可以作为沸石中的路易斯酸位点，由于其极度扭曲的局部环境而“核磁共振不可见”。在这里，我们提供了一种可行且可靠的方法，通过灵敏度增强的二维 (2D) 多核相关 NMR 实验结合三甲基氧化膦 (TMPO) 来阐明脱水 H-ZSM-5 沸石中三配位骨架 Al 的酸性性质探针分子。已明确识别出两种类型的三配位骨架 Al 位点，共 11 个。Brønsted 和 Lewis 酸位点总数的 6%。此外，发现由三配位骨架 Al 位点和 Brønsted 酸位点之间的紧密空间接近产生的协同效应导致沸石中产生超酸性（酸强度高于 100% H2SO4）。
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