NSF-DFG Echem: CAS: Cooperativity Between Immobilized Redox Mediators for Selective Anodic Biomass Valorization

在化学系化学催化项目的支持下，科罗拉多大学博尔德分校的Adam Holewinski和Wei Zhang正在研究催化材料的新设计。该项目还涉及来自德国的罗斯托克大学的合作者。电催化剂促进电能和化学键的相互转换。这些转变对于通过化学燃料储存和提取可再生电力以及合成依赖于大量能量输入的大容量化学产品越来越感兴趣。有效的催化剂，如在自然界中发现的酶，通常依赖于多个化学官能团之间的协同作用，以引导反应朝向所需的产物。该项目的重点是设计合作的电催化剂，其中两个物种一起工作，以驱动比单独使用任何一个物种所需的电输入更少的反应。工作将集中在合成催化剂上，其中每个介体都附着在聚合物上，使它们保持紧密接近。虽然获得的知识基本上适用于广泛的重要化学品，但该项目将从模型反应（例如简单醇选择性氧化为醛）发展到涉及更高价值底物的反应。特别是，将以使用来自生物质的原料生产用于绿色塑料的环境友好的单体化合物为目标。从应用的角度来看，可扩展的氧化过程的发展可能会改变化学生产电解的经济前景。教育一体化举措将包括将不同的本科生纳入研究过程，并继续开发基于网络的教育模块。与德国罗斯托克大学的国际合作是该项目的一个关键组成部分，参与的研究生将有机会进行访问研究。该项目是通过“NSF-DFG电合成和电催化牵头机构活动（NSF-DFG EChem）”的机会获得的，这是一个涉及NSF和德国研究共同体（DFG）的合作招标。在这个合作研究奖下，科罗拉多大学博尔德分校的Adam Holewinski和Wei Zhang将研究催化材料的新设计。设计具有多个参与官能团的定制基底结合环境难以用均相分子催化剂实现，并且使用非均相催化剂材料甚至更具挑战性。该提案旨在理解和开发合作的电催化位点，由有机氧化还原介体和氧化还原活性金属中心组成，两者都进行电子转移。这项工作借鉴了最近的示范均相氧化还原介体机制，其中一个两电子氧化是通过提取一个电子到两个介体中的每一个，通过避免更高的介体氧化态，降低必要的应用电位，通常访问实现两个电子氧化。该机制从根本上不同于更常见的协同性例子，如金属配体。该合作研究小组旨在发展有效地将此类合作催化剂固定到（a）可溶性（但易于分离）聚合物和（B）异质电极上所需的基本理解和方法。这两个平台提供了互补的手段，以确定由固定施加的限制，并了解如何最好地保持合作性。机理研究将被用来理解复杂程度不同的探针反应中的电氧化协同性：（i）伯醇到醛的选择性转化;（ii）氧化5-（羟甲基）-糠醛（HMF）至二甲酰基呋喃（DFF）（用于绿色塑料沿着其它化学应用的单体），和（iii）多电子氧化以产生羧酸-特别是HMF至2，5-呋喃二甲酸（FDCA），另一种需要醛和醇基团氧化的单体。这些反应对于不断扩大的生物质价值评估领域至关重要，同时也是了解实现合作性的关键约束条件的信息试验平台。这项工作进一步解决了与复杂材料电催化活性基准测试相关的广泛问题，旨在为活性表征建立严格的先例。该奖项反映了NSF的法定使命，并被认为值得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来支持。

With the support of the Chemical Catalysis program in the Division of Chemistry, Adam Holewinski and Wei Zhang of the University of Colorado-Boulder are studying new designs for catalytic materials. The project also involves collaborators from Rostock University in Germany. Electrocatalysts facilitate the interconversion of electrical energy and chemical bonds. These transformations are increasingly of interest for storage and extraction of renewable electricity via chemical fuels, as well as for synthesizing high volume chemical products that rely on large energy inputs. Efficient catalysts such as the enzymes found in nature often rely on cooperative interactions among multiple chemical functional groups to steer a reaction toward desired products. This project is focused on designing cooperative electrocatalysts where two species work together to drive a reaction with less electrical input than would be required from either species alone. Work will center on synthesizing catalysts where each mediator is attached to a polymer such that they remain in close proximity. While the knowledge to be gained is fundamentally applicable for a wide range of important chemistries, the project will progress from model reactions (e.g. selective oxidation of simple alcohols to aldehydes) to reactions involving higher value substrates. In particular, production of environmentally friendly monomer compounds for green plastics will be targeted using raw materials derived from biomass. From an applied perspective, the development of scalable oxidative processes could alter the economic landscape of electrolysis for chemical production. Educational integration initiatives will include inclusion of diverse undergraduates in the research process and continued development of web-based educational modules. International collaboration with Rostock University in Germany is a key component of the project and participating graduate students will have the opportunity for visiting research. The project was awarded through the "NSF-DFG Lead Agency Activity in Electrosynthesis and Electrocatalysis (NSF-DFG EChem)" opportunity, a collaborative solicitation that involves NSF and Deutsche Forschungsgemeinschaft (DFG).Under this collaborative research award, Adam Holewinski and Wei Zhang of the University of Colorado-Boulder will study new designs for catalytic materials. Designing tailored substrate binding environments with multiple participant functional groups is difficult to achieve with homogeneous molecular catalysts, and even more challenging using heterogeneous catalyst materials. This proposal aims to understand and develop cooperative electrocatalytic sites, comprised of an organic redox mediator and redox-active metal center, both performing electron transfer. The work draws on recent demonstrations of homogeneous redox mediator mechanisms in which a two-electron oxidation is achieved by extraction of one electron into each of two mediators, lowering the necessary applied potentials by avoiding higher mediator oxidation states, normally accessed to achieve two electron oxidation. The mechanism is fundamentally distinct from more common examples of cooperativity, such as metal-ligand. The collaborative research team seeks to develop the fundamental understanding and methodologies needed to effectively immobilize such cooperative catalysts onto (a) soluble (but easily separated) polymers and (b) heterogeneous electrodes. These two platforms provide complementary means to identify constraints imposed by immobilization and understand how best to retain cooperativity. Mechanistic studies will be used to understand electro-oxidation cooperativity in probe reactions of variable complexity: (i) selective conversion of primary alcohols to aldehydes; (ii) oxidation of 5-(hydroxymethyl)-furfural (HMF) to diformylfuran (DFF) (a monomer for green plastics along with other chemical applications), and (iii) multi-electron oxidation to generate carboxylic acids—particularly HMF to 2,5-furandicarboxylic acid (FDCA), another monomer requiring both aldehyde and alcohol group oxidation. These reactions are critical to the expanding field of biomass valorization and simultaneously serve as an informative testbed for understanding the key constraints to realize cooperativity. The work further addresses widespread issues related to benchmarking of electrocatalytic activity on complex materials, aiming to establish rigorous precedents for activity characterization.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.