CAREER: Photocatalytic Transfer Hydrogenation of CO2 Using Transition Metal Cluster Arrays

在化学系化学催化项目的支持下，克里斯托弗·H·俄勒冈州大学的亨登正在研究过渡金属簇介导的光催化二氧化碳（CO2）还原。二氧化碳还原是一个重要的化学反应，因为它可以降低大气中的二氧化碳水平，同时还可以形成甲酸和甲醛等有价值的产品。CO2转化是一种困难的化学转化，因为所需的产物（例如甲酸和甲醛）是相互竞争形成的，形成它们所需的质子和电子的数量不同。为了克服这个问题，亨登博士将使用计算建模来研究无机团簇对CO2的光催化还原，这将为反应提供精确的质子和电子数量。该研究将研究这些金属簇如何用于饥饿反应物（H·）的氢化反应以选择目标产物，并证明支持金属簇的配体允许金属位点的能量调节。如果成功的话，这项工作有可能指导实验人员实现更有选择性的条件，将CO2还原为所需的产品。此外，这种计算工作可能证明在其他有问题的氢化，困扰的选择性问题，包括烯烃和炔的区域选择性还原有用。这项工作将与亨登博士现有的饮料提取物电催化方案协同作用，这是一个成功的方案，通过咖啡的透镜教授基础化学和物理学。该奖项将支持为非传统学生开发正式课程，该课程将开源并由社区维护。虽然最重要的CO2还原反应可以通过传统的H2氢化来促进，但选择性可以通过使用其他H源来实现。一种有希望的途径涉及转移氢化，即氢从一种物质交换到另一种物质。该提案旨在证明选择性CO2转移氢化（还原）可以使用金属有机框架（MOF）中原子精确的无机簇来实现。在这个奖项中，亨登博士将使用计算化学来检查一个家庭的非均相多核过渡金属催化剂，并将研究氢从供体（例如醇，水等）提取的一般机制。并转移到受体（例如CO2）。反应机理可能取决于供体/催化剂/受体的pKa差异以及它们的氧化还原电位。从这些研究中，亨登小组将通过簇调制寻找具有改进的化学选择性的目标MOF簇，其中可用氢原子的数量可调。总之，这些研究渴望产生一个一般的设计原则，选择供体，受体，和基于MOF的催化剂，基于电子能量排列。通过与实验人员的合作，该工作旨在产生一系列CO2还原光催化剂，这些光催化剂的H·来自丰富的捐助者。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。

With support from the Chemical Catalysis Program in the Division of Chemistry, Christopher H. Hendon of the University of Oregon is studying photocatalytic carbon dioxide (CO2) reduction mediated by transition metal clusters. Carbon dioxide reduction is an important chemical reaction because it can reduce atmospheric CO2 levels, while also forming valuable products like formic acid and formaldehyde. CO2 conversion is a difficult chemical transformation because the desired products (e.g. formic acid and formaldehyde) are formed in competition with one another, differing in the number of protons and electrons required to form them. To overcome this problem, Dr. Hendon will use computational modeling to study photocatalytic reduction of CO2 with inorganic clusters, which will provide precise numbers of protons and electrons for the reaction. The research will examine how these metal clusters can be used to starve hydrogenation reactions of reactants (H•) to select for target products, and demonstrate that the ligands that support the metal clusters allow for energetic tuning of the metal sites. If successful, this work has the potential to guide experimentalists to achieve more selective conditions for CO2 reduction to the desired product. Moreover, this computational work may prove useful in other problematic hydrogenations, plagued by selectivity issues, including the regioselective reduction of alkenes and alkynes. This work will synergize with Dr. Hendon’s existing program in electrocatalysis of beverage extracts, a successful program that teaches fundamental chemistry and physics through the lens of coffee. This award will support the development of a formal curriculum for non-traditional students, that will be made open-source and community-maintained.While the the all-important CO2 reduction reaction can be promoted through conventional hydrogenation with H2, selectivity can be achieved by using other H-sources. One promising route involves transfer hydrogenation, whereby hydrogen commutes from one species to another. This proposal seeks to demonstrate that selective CO2 transfer hydrogenation (reduction) can be achieved using atomically precise inorganic clusters in metal-organic frameworks (MOFs). In this award, Dr. Hendon will use computational chemistry to examine a family of heterogeneous polynuclear transition metal catalysts and will study the general mechanism in which hydrogen is extracted from donors (e.g. alcohols, water, etc.) and transferred to acceptors (e.g. CO2). The reaction mechanism likely depends on differences in pKa of the donor/catalyst/acceptor, as well as their redox potentials. From these studies, the Hendon group will search for target MOF clusters with improved chemical selectivity with tunable numbers of available hydrogen atoms through cluster modulation. Together, these studies aspire to yield a general design principle for selection of donor, acceptor, and MOF-based catalysts, based on electron energy alignments. Through collaboration with experimentalists the work aims to generate a family of CO2 reduction photocatalysts that source their H• from abundant donors.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.