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New Experimental Approaches for DNP Surface Enhanced Quadrupolar NMR Spectroscopy at Very High Magnetic Field

极高磁场下 DNP 表面增强四极核磁共振波谱的新实验方法

基本信息

批准号：
426792711
负责人：
Dr. Monu Kaushik, Ph.D.
金额：
--
依托单位：
ISA - Institut des Sciences Analytiques
依托单位国家：
德国
项目类别：
Research Fellowships
财政年份：
2019
资助国家：
德国
起止时间：
2018-12-31 至 2020-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/426792711?language=en
关键词：
New Experimental Approaches DNP Surface

项目摘要

NMR spectroscopy is the method of choice to characterize the atomic-scale structure of surfaces whenever possible, but the detection limit of NMR is far too low to allow many modern materials to be examined. Because it provides dramatic sensitivity enhancement, solid-state Dynamic Nuclear Polarization (DNP) NMR is currently emerging as a powerful tool to study samples previously inaccessible to NMR, and notably to selectively enhance the NMR signals from surfaces using an approach called DNP SENS (DNP Surface Enhanced NMR Spectroscopy). A vast majority of the NMR-active isotopes are subjected to quadrupolar interaction. For investigation of materials with quadrupolar probe nuclei, the use of high magnetic fields provide a quadratic gain in both resolution and sensitivity. However, most modern DNP experiments rely on a polarization transfer scheme whose efficiency scales with the inverse of the magnetic field strength B0 and is significantly reduced at fast Magic Angle Spinning (MAS). This project aims at implementing new spectroscopic approaches for the atomic-scale structural characterization of challenging surfaces by exploring new frontiers of DNP surface enhanced quadrupolar NMR spectroscopy at very high magnetic field and fast MAS. The project tackles several basic research issues in the field of characterization tools and in materials science. In particular, it will address the following challenges: i) the introduction of innovative sample preparation strategies for high-field DNP that are expected to outperform today’s protocols. ii) the implementation of advanced solid-state quadrupolar NMR methods under DNP conditions. Here we aim for implementation and the in-depth performance analysis of both J-based and dipolar based heteronuclear (1H-27Al/29Si-27Al) and homonuclear (27Al-27Al) correlation techniques, as well as the development of proton-detected experiments. iii) Characterization of surface and interface of aluminosilicates. The developed approaches for sample formulation and NMR techniques will be applied to the characterization of amorphous silica-alumina, for which the structure of the so far invisible but catalytically important highly reactive 27Al surface sites remains a matter of debate in the field of heterogeneous catalysis. Such atomic-scale structure details of surfaces in materials are usually not amenable to any other technique. The overall results of this project will provide innovative spectroscopic tools to probe with unprecedented sensitivity and resolution of molecular structures of surfaces. This proposal will lean on a unique DNP instrumentation available in Lyon at 9.4 and 18.8 T, on recent advanced in the design of radicals for DNP at very high magnetic field and on a first-class, consortium in solid-state NMR and materials science. This is a timely and ambitious project that will directly extend the areas of application of this spectroscopy, and substantially contribute to fundamental knowledge in catalysis.

核磁共振光谱是尽可能表征表面原子级结构的首选方法，但核磁共振的检测下限太低，无法对许多现代材料进行检测。由于固态动态核极化(DNP)核磁共振具有显著的灵敏度增强作用，目前已成为研究以前核磁共振无法获得的样品的有力工具，尤其是使用一种称为DNP SENS(DNP表面增强核磁共振光谱)的方法选择性地增强来自表面的核磁共振信号。绝大多数具有核磁共振活性的同位素受到四极相互作用的影响。对于具有四极探测核的材料的研究，使用高磁场在分辨率和灵敏度方面都提供了二次增益。然而，大多数现代DNP实验依赖于极化转移方案，其效率与磁场强度B0成反比，并且在快速魔角旋转(MAS)时效率显著降低。该项目旨在通过探索DNP表面增强的四极核磁共振谱在极高磁场和快速MAS下的新前沿，实现用于挑战表面的原子级结构表征的新的光谱方法。该项目解决了表征工具和材料科学领域的几个基础研究问题。特别是，它将解决以下挑战：i)为高场DNP引入创新的样品制备战略，预计这些战略的表现将优于目前的协议。二)在DNP条件下实现先进的固态四极核磁共振方法。在这里，我们的目标是实现和深入分析J基和偶极基异核(1H-27Al/29Si-27Al)和同核(27Al-27Al)关联技术，以及质子探测实验的发展。Iii)铝硅酸盐的表面和界面的表征。所开发的样品配制方法和核磁共振技术将被应用于非晶态硅铝的表征，对于非晶态硅铝来说，迄今看不见但具有重要催化活性的27Al表面中心的结构在多相催化领域仍然是一个有争议的问题。材料表面的这种原子尺度的结构细节通常不适用于任何其他技术。该项目的总体成果将提供创新的光谱工具，以前所未有的灵敏度和分辨率探测表面的分子结构。这项提议将依赖于里昂独特的9.4和18.8T的DNP仪器，基于最近在非常高磁场下为DNP设计的先进自由基，以及一流的固体核磁共振和材料科学联盟。这是一个及时而雄心勃勃的项目，将直接扩大该光谱学的应用领域，并对催化基础知识做出重大贡献。