DMREF: Collaborative Research: GOALI: Multiscale Design of Zeolite Sites for Precise Catalytic Transformations

沸石是一种晶体状固体材料，含有分子大小的孔隙，因此在汽油精炼和柴油汽车尾气净化等方面有着广泛的应用。沸石是天然存在的，但技术材料是大规模合成生产的。特定沸石的性质部分取决于其孔隙大小和形状，部分取决于材料中的化学元素；然而，人们对这些关系的具体情况知之甚少。因此，名义上相同的沸石在给定的应用中可能表现出截然不同的性能。该项目的总体目标是开发计算机模型和实验协议，以提高我们在沸石合成过程中精确定位沸石孔内元素位置的能力。这种理解有望导致在当前应用中具有优异性能的材料，更持久，更耐用，并且可以执行今天不可能实现的功能。为了实现这些目标，它汇集了一组具有沸石合成和表征，实验和分子尺度计算机模型以及工业和学术实验室专业知识的研究人员。它提供了新的建模协议和新材料，同时在多样化的协作环境中培养学生，为化学技术的职业生涯做好准备。该项目特别侧重于结晶铝硅酸盐沸石。在这些材料中，沸石骨架内的铝杂原子是阴离子电荷中心。越来越多的证据表明，这些铝中心的相对接近性对沸石的最终性能有重大影响，特别是它们在Bronsted酸催化（甲醇脱水）和氧化还原催化（NOx的选择性催化还原）中的功能。主要假设是，在合成过程中存在的带阳离子的结构导向剂（SDAs）对给定沸石晶格内Al原子的位置有决定性影响，其影响可以从SDAs与预形成的铝取代沸石之间的相互作用中推断出来，并且相同的建模方法可以用于预测合成后离子交换过程中的物种形成。为了验证这些假设，该项目开发了经典和第一性原理模型，以预测一系列沸石框架中有机SDAs和无机阳离子与硅铝比的沸石组成相图。这些模型通过对实验室合成的沸石的实验观察进行了验证，使用了非原位光谱和化学表征以及催化条件下的动力学评估，并根据第一性原理和微动力学模型预测了Al原子位置和性质之间的关系。该项目推进了沸石材料在计算/实验和学术/工业协作环境中具有实际意义的催化反应的计算设计。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Zeolites are a class of crystalline, solid materials that contain pores of the size of molecules, lending to their wide use in applications such as gasoline refining, and cleaning exhaust coming from diesel vehicles. Zeolites are naturally occurring, but technological materials are produced synthetically and at large scale. The properties of a particular zeolite are determined in part by its pore size and shape, and in part by the chemical elements in the material; however, specifics of these relationships are poorly understood. As a result, nominally the same zeolites may show vastly different performance in a given application. The overarching aim of this project is to develop computer models and experimental protocols that increase our ability to precisely locate the positions of elements within the zeolite pores during the zeolite synthesis process. This understanding is expected to lead to materials that have superior performance in current applications, are longer-lasting and more durable, and can perform functions that are not possible today. To achieve these ends, it brings together a team of researchers with expertise in zeolite synthesis and characterization, in experiment and in molecular-scale computer models, and from industrial and academic laboratories. It delivers new modeling protocols and new materials, while simultaneously training students in a diverse, collaborative environment who are well prepared for careers in chemical technologies.The project focuses in particular on crystalline aluminosilicate zeolites. In these materials, aluminum heteroatoms within the zeolite framework are anionic charge centers. Increasing evidence indicates that the relative proximity of these aluminum centers has a significant impact on the ultimate properties of the zeolite, in particular in their function in Bronsted acid catalysis (methanol dehydration) and in redox catalysis (the selective catalytic reduction of NOx). The main hypotheses are cationically charged structure-directing agents (SDAs) present during the synthesis process have a determining effect on the location of those Al atoms within a given zeolite lattice, their effect can be inferred from the interactions between SDAs and the pre-formed, aluminum-substituted zeolite, and the same modeling approach can be used to predict speciation during post-synthetic ion exchange. To test these hypotheses, the project develops classical and first-principles models to predict zeolite compositional phase diagrams for organic SDAs and inorganic cations vs silicon-to-aluminum ratio in a series of zeolite frameworks. These models are validated against experimental observation on laboratory-synthesized zeolites, using both ex situ spectroscopic and chemical characterization as well kinetic evaluations under catalytic conditions, and informed by first-principles and microkinetic modeling predictions of the relationship between Al atom location and properties. The project advances the computational design of zeolite materials in the context of practically significant catalytic reactions in a computation/experiment and academic/industrial collaborative setting.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.