Characterizing Structures and Intra-/Intermolecular Forces in Molecular CO2 Reduction Catalysts and Reaction Intermediates by Infrared Spectroscopy of Cryogenic Ions

许多人认为，创造碳中和、可持续的能源经济是不久的将来要开发的最重要的新技术之一。将二氧化碳（CO2）转化为化学可用燃料是实现这一目标的一种有希望的方法。这些方法难以实施，并且它们需要催化剂的辅助，即，通过降低将二氧化碳转化为燃料所需能量的分子或材料。为了开发具有成本效益的催化剂，我们需要了解CO2如何与催化剂分子相互作用。 在这个由化学系化学结构动力学和机制（CSDM-A）项目资助的项目中，位于博尔德的科罗拉多大学的J. Mathias Weber教授正在使用最先进的质谱和激光光谱技术来研究CO2与催化剂分子的相互作用。 感兴趣的催化剂是包含金属如钴（Co）和铼（Re）的分子，其被包含其它元素（例如碳（C）、氧（O）、氮（N））的结构包围。 周围的结构影响CO2如何与金属原子结合（关键的催化过程起源于CO2-金属原子相互作用）。 这些金属催化剂“络合物”是离子的（它们具有电荷），这意味着它们可以使用质谱仪进行分类和浓缩。 将所需的离子催化剂络合物冷却至非常低的温度（低至5开氏度（K），或零下450华氏度）。 在这些低温下，CO2分子与催化剂络合物结合。 一旦CO2-金属络合物形成，红外激光被用来测量这些络合物的振动。 从振动，复合物的结构可以推断。这种方法可以探测其反应中的关键步骤，从而可以组装催化剂如何发挥作用的详细机制。这项工作的更广泛的影响包括对开发新的化学燃料来源的潜在社会效益，对环境的影响小，以及对研究生研究人员进行先进的实验和计算技术的培训。此外，韦伯集团正在开发一个基于网络的二氧化碳转化模拟，将实验室研究带入课堂，旨在提高学生对催化的理解。在该项目中，Weber小组表征了用于二氧化碳转化的分子催化剂的红外光谱，以及与涉及此类催化剂的催化循环相关的其他物质。所研究的催化剂是通过电喷雾电离产生的带电分子（离子）。它们与二氧化碳、质子供体和溶剂的复合物在一系列温控离子阱中制备，并在飞行时间质谱仪中分离。用来自可调红外光源的脉冲光照射靶分子。它们在光子吸收时碎裂，并且在第二质量分析步骤中检测碎片。研究中的复合物的振动光谱测量监测片段，同时调谐红外波长。光谱产生的信息的结构和分子间的力量控制的功能的催化剂。光谱与量子化学计算一起，提供了对二氧化碳电化学转化为其他更有价值分子的化学机理的深入了解。该奖项反映了NSF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。

The generation of a carbon-neutral, sustainable energy economy has been recognized by many as one of the most important new technologies to be developed in the near future. The conversion of carbon dioxide (CO2) into chemically useable fuels is a promising approach to attain this goal. Such processes are difficult to implement, and they need to be assisted by catalysts, i.e., by molecules or materials that lower the energy required to convert CO2 into fuel. In order to develop cost-effective catalysts, we need to understand how CO2 interacts with catalyst molecules. In this project funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Professor J. Mathias Weber of the University of Colorado at Boulder is using a state-of-the-art combination of mass spectrometric and laser spectroscopy techniques to study the interactions of CO2 with catalyst molecules. The catalysts of interest are molecules that contain metals such as cobalt (Co) and rhenium (Re) surrounded by structures containing other elements (for example carbon (C) , oxygen (O), nitrogen (N)). The surrounding structures influence how CO2 binds to the metal atom (key catalytic processes originate in the CO2-metal atom interaction). These metal catalyst "complexes" are ionic (they possess electric charge), which means they can be sorted and concentrated using a mass spectrometer. The desired ionic catalyst complexes are cooled to very low temperatures (as low as 5 degrees Kelvin (K), or minus 450 degrees Fahrenheit). At these low temperatures, CO2 molecules bind to the catalyst complexes. Once the CO2-metal complexes are formed, infrared laser light is used to measure the vibrations of these complexes. From the vibrations, the structures of the complexes can be inferred. This approach enables probing key steps in their reactions, allowing the assembly of detailed mechanisms of how the catalysts function. The broader impacts of this work include potential societal benefits towards the development of new sources of chemical fuels with low environmental impact, as well as the training of graduate student researchers in advanced experimental and computational techniques. Moreover, the Weber group is developing a web-based simulation of carbon dioxide conversion, transporting the laboratory research into the classroom, with the aim to enhance student understanding of catalysis. In this project, the Weber group characterizes the infrared spectra of molecular catalysts for the conversion of carbon dioxide, as well as other species relevant for the catalytic cycle involving such catalysts. The catalysts under study are charged molecules (ions), generated by electrospray ionization. Their complexes with carbon dioxide, proton donors, and solvents are prepared in a series of temperature-controlled ion traps, and isolated in a time-of-flight mass spectrometer. The target molecules are irradiated with pulsed light from a tunable infrared light source. They fragment upon photon absorption, and the fragments are detected in a second mass analysis step. The vibrational spectra of the complexes under study are measured by monitoring fragments while tuning the infrared wavelength. The spectra yield information on the structures and intermolecular forces governing the function of the catalysts. Together with quantum chemical calculations, the spectra provide mechanistic insight into the chemistry at play in electrochemical conversion of carbon dioxide into other, more valuable molecules.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.