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首页> 外文期刊>Chemistry: A European journal >Proton Acidity and Proton Mobility in ECR-40, a Silicoaluminophosphate that Violates L?wenstein's Rule
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Proton Acidity and Proton Mobility in ECR-40, a Silicoaluminophosphate that Violates L?wenstein's Rule

机译：ECR-40中的质子酸度和质子迁移率，侵犯L的硅铝磷酸盐

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摘要

The silicoaluminophosphate zeotype ECR-40 contains linkages of AlO_4 tetrahedra via a common oxygen atom, thereby violating the famous "L?wenstein's rule". In this work, a combination of static density functional theory (DFT) calculations and DFT-based ab-initio molecular dynamics (AIMD) simulations were employed to study the acidity and mobility of protons associated with such unusual linkages. It was found that the Al-O-Al linkages are preferentially protonated, as deprotonation causes a local accumulation of negative charge. The protons at these linkages possess a somewhat lower Br?nsted acidity than those at Si-O-Al links. AIMD simulations for fully hydrated ECR-40 predicted a partial deprotonation of the Al-O-Al linkages, whereas Si-O-Al linkages were fully deprotonated. Frequently, a coordination of water molecules to framework Al atoms was observed in the vicinity of the Al-O-Al links. Hence, these linkages appear prone to break upon dehydration, potentially explaining why L?wenstein's rule is mostly obeyed in materials formed in aqueous media.
机译：硅铝磷酸酶型ECR-40通过共同的氧原子含有AlO_4 Tetrahedra的键，从而侵犯着名的“L？Wenstein的规则”。在这项工作中，采用静态密度泛函理论（DFT）计算和基于DFT的AB-Initio分子动力学（AIMD）模拟的组合研究与这种不寻常的联系相关的质子的酸度和迁移率。发现优先质子化Al-O-Al键，因为去质子化导致局部积累负电荷。这些连杆处的质子具有比Si-O-Al链接的酸度稍微较低的酸度。用于全水合ECR-40的AIMD模拟预测Al-O-Al键的部分去质子，而Si-O-Al键完全脱向。通常，在Al-O-Al链路附近观察到水分子与框架Al原子的协调。因此，这些联动似乎易于在脱水时破裂，潜在地解释为什么L？温斯坦的规则大多是在水性介质中形成的材料中的措施。

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