High Resolution ESR Spectroscopy for Catalysis Research

电子自旋共振(ESR)谱是一种磁共振技术，用于分析任何包含未配对电子的系统。因此，它是研究顺磁性化合物和自由基的一种极其强大、先进和通用的工具。然而，在大多数商业仪器采用的常见微波频率(9.5 GHz)下，ESR的一个缺点是观察到具有低g各向异性的自由基的重叠信号，特别是在无序系统中，或者由包含不止一个未配对电子的顺磁系统产生的复杂光谱。因此，关于自由基的身份的大量信息可能会丢失，并且光谱本身可能很难解释。通过在较高频率(94 GHz，称为W频段ESR)下进行ESR测量，可以更容易地提取这些信息，并大大简化频谱分析的简易性。W波段ESR被认为是一种强大的补充光谱技术，具有独特的能力，通过提供对含有未配对电子的系统的更高分辨率和电子洞察，提供关于顺磁系统结构和动力学的信息。因此，高分辨率ESR是对传统ESR工具箱的一个重要补充，它提供了更完整的自旋哈密顿量描述，并详细描述了液体中的反应性自由基和固态和冷冻溶液中的顺磁性络合物。在这个项目中，我们将在卡迪夫大学安装一台连续波(CW)W波段ESR光谱仪，这将是专门为催化研究项目而设置的。CW仪器将使我们能够对顺磁性金属中心、表面和体缺陷、局域电子、掺杂剂、自旋标记/探针和自由基(与均相或非均相催化系统相关)进行更先进的ESR测量，主要是在固体和液体中、在气固和液-固界面、在高温和低温以及光解条件下。催化是任何技术的终极挑战，反应发生在特定的原子位置，在快速的时间尺度上，通常在复杂的介质中。这需要利用先进的光谱方法，不仅可以探测电子结构、对称性、自旋态和配位数的变化，而且可以揭示催化循环中涉及的反应中间体的动力学和性质。W波段ESR仪器可以获取含有未配对电子的催化系统的所有这些关键信息，因此将为英国的催化研究提供重要的额外能力。该仪器将为催化界提供专门用于均相和多相催化研究项目的ESR仪器，即检测多相催化中的活性氧物种，了解表面结合的自由基和缺陷在催化和光催化中的参与，研究氧化还原活性中心在催化中的作用和均相金属有机催化的表征，以及表征掺杂到微孔材料和受限环境中的过渡金属离子。这些项目工作包将通过与加的夫催化研究所(CCI)、英国催化中心、GW4大学联盟和其他英国催化团体和工业合作伙伴的关键利益相关者和项目合作伙伴进行合作。该仪器将由PI和COI管理，由加的夫大学和Bruker UK Limited提供支持，并将为英国的科学设备基础设施增加必要的额外能力。从这个项目中获得的见解最终将用于开发下一代改进的、更便宜和更高效的催化剂。

Electron Spin Resonance (ESR) spectroscopy is a magnetic resonance technique used in the analysis of any system containing unpaired electrons. It is therefore an extremely powerful, advanced and versatile tool for the study of paramagnetic compounds and free radicals. However, one drawback of ESR that is often encountered at the common microwave frequency (9.5 GHz) adopted by most commercial instruments, is the overlapping signals observed for radicals with low g-anisotropy, particularly in disordered systems, or the complex spectra arising from paramagnetic systems containing more than one unpaired electron. As a result, a significant amount of information on the identity of the radical can be lost and the spectra themselves can be very difficult to interpret. This information can be more readily extracted, and the ease of spectral analysis considerably simplified, by performing the ESR measurements at higher frequencies (94 GHz, referred to as W-band ESR). W-band ESR is regarded as a powerful complimentary spectroscopic technique with unique capabilities for providing information on the structure and dynamics of paramagnetic systems, by offering higher resolution and electronic insights into systems bearing unpaired electrons. High resolution ESR is thus an essential compliment to the traditional ESR tool-box in providing a more complete description of the spin Hamiltonian and the detailed characterization of reactive free radicals in the liquid phase and paramagnetic complexes in the solid state and frozen solution. In this project, we will install a continuous wave (CW) W-band ESR spectrometer in Cardiff University, which will be specifically set-up for projects in catalysis research. The CW instrument will enable us to perform more advanced ESR measurements of paramagnetic metal centres, surface and bulk defects, localised electrons, dopants, spin labels/probes and free radicals (of relevance to homogeneous or heterogeneous catalytic systems), primarily in solids & liquids, at the gas-solid and liquid-solid interface, at high and low temperatures and under photolysis conditions. Catalysis represents the ultimate challenge for any technique, with reactions occurring at specific atomic sites, at fast times scales and often in complex media. This requires the utilization of advanced spectroscopic methodologies that can probe not only the changes in electronic structure, symmetry, spin states and coordination numbers, but also that can reveal insights into the dynamics and nature of the reactive intermediates involved in the catalytic cycle. The W-band ESR instrument can access all of this key information for catalytic systems bearing unpaired electrons, and thus will provide an important additional capability for catalysis research in the UK. The instrument will provide the catalysis community access to an ESR instrument dedicated for research projects in homogeneous and heterogeneous catalysis, namely in the detection of reactive oxygen species in heterogeneous catalysis, understanding the involvement of surface bound radicals and defects in catalysis and photocatalysis, investigating the role of redox active centres in catalysis & the characterization of homogeneous organometallic catalysis, and characterising the transition metal ions doped into microporous materials and confined environments. These project work-packages will be undertaken through collaborations with key stakeholders and project partners in the Cardiff Catalysis Institute (CCI), the UK Catalysis Hub, the GW4 Alliance of Universities and other UK catalysis groups and industrial partners. The instrument will be managed by the PI and CoI, is supported by Cardiff University and Bruker UK Limited, and will add an essential additional capacity to the UK scientific equipment infrastructure. The insights gained in this project will ultimately be used to develop the next generation of improved, cheaper and more efficient catalysts.