Hyperpolarized Zero-to-Ultralow-Field Nuclear Magnetic Resonance

我们建议结合核磁共振（NMR）波谱和成像的两个最新发展-零到超低场（ZULF）核磁共振和超极化样品核磁共振-建立一个新的研究催化过程的平台。为了优化化工过程，需要在实际条件下研究催化作用。在这方面，传统的高场核磁共振波谱和成像是有用的工具，因为它们同时提供了关于样品的化学信息，并具有化学特异性成像质量流动或运输的能力。然而，由于磁化率的扩大，化学特异性往往会丧失，而且有限的射频穿透深度使金属容器无法使用。需要施加强磁场也限制了可移植性，并限制了可以研究的系统的大小。相比之下，ZULF NMR不受磁化率效应的影响，这意味着即使样品是异质或双相的，也能保持化学特异性。此外，与传统的核磁共振相比，显著降低的信号频率使得“透视”导电材料（包括金属容器）成为可能。我们将探索ZULF NMR作为一种方法来进行operando反应监测。为了解决ZULF核磁共振信号强度低的问题，我们采用了对氢基超极化。氢气可以很容易地以非平衡核自旋态（对氢）制备，如果它是与对氢化学反应形成的，或者是与金属中心上活化的对氢分子可逆接触，则会导致探针分子的核磁共振信号显著增强（超极化）。增强信号允许探针分子在ZULF核磁共振条件下进行研究。我们将使用这些超极化探针开发ZULF NMR作为一种方法来监测均匀溶液中的化学反应，以及研究多孔催化剂和吸附剂表面上具有活性中心的超极化分子的相互作用。最后，在本研究中，我们将使用对氢不仅作为超极化源，而且作为化学反应物和机械探针。加氢反应是在工业规模上进行的，如果催化机制得到更好的理解，这些过程的效率可以大大提高。对氢只有在双加成时才会导致信号增强，这可以用来深入了解潜在的反应机制，以及优化多相催化剂，其中具有更好定义和结构的活性中心的单位点加氢是一个重要目标。因此，我们将采用本项目的先进方法，结合ZULF NMR和对苯二酚基自旋超极化的信号增强，研究固体负载金属催化剂上的加氢反应机理。

We propose to combine two recent developments in nuclear magnetic resonance (NMR) spectroscopy and imaging — zero- to ultralow-field (ZULF) NMR and NMR with hyperpolarized samples — to establish a new platform for studying catalytic processes.For the optimization of chemical industrial processes, it is desirable to study catalysis under realistic conditions. Conventional high-field NMR spectroscopy and imaging have been useful tools in this regard, as they simultaneously provide chemical information about a sample and the ability to image mass flow or transport with chemical specificity. However, chemical specificity is often lost due to magnetic-susceptibility broadening, and the limited radiofrequency penetration depth precludes the use of metal containers. The need to apply a strong magnetic field also limits portability and constrains the size of systems that can be investigated. In contrast, ZULF NMR is free from susceptibility effects, which means that chemical specificity is retained even when the sample is heterogeneous or biphasic. Furthermore, the significantly lower signal frequencies compared to conventional NMR make it possible to ‘see through’ conductive materials Including metal containers.We will explore ZULF NMR as a method to perform operando reaction monitoring. To address the low signal strength of ZULF NMR, we employ parahydrogen-based hyperpolarization. Hydrogen gas can be readily prepared in a nonequilibrium nuclear spin state (parahydrogen), which leads to dramatically enhanced (hyperpolarized) NMR signals of a probe molecule if it is either formed by chemical reaction with parahydrogen or brought reversibly in a contact with activated parahydrogen molecule on a metal centre. The enhanced signals allow the probe molecules to be studied under ZULF NMR conditions. We will use these hyperpolarized probes to develop ZULF NMR as a method to monitor chemical reactions in homogeneous solutions, as well as studying the interaction of hyperpolarized molecules with active centres on surfaces of porous catalysts and sorbents.Finally, in this study we will use parahydrogen not only as the hyperpolarization source but also as the chemical reactant and a mechanistic probe. Hydrogenation reactions are carried out on an industrial scale, and if the catalytic mechanisms were better understood, the efficiency of these processes could be vastly improved. Parahydrogen only leads to enhanced signals when the addition is pairwise, which can be utilized to provide insight into the underlying reaction mechanisms, as well as the optimization of heterogeneous catalysts, for which single-site hydrogenation with better-defined and structured active centres is an important goal. We will therefore investigate hydrogenation reaction mechanisms on solid supported metal catalysts by applying the advanced approach of this project which combines ZULF NMR with signal enhancement by parahydrogen-based spin hyperpolarization.