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亚当·霍勒文斯基和张伟正在研究催化材料的新设计。该项目还包括来自德国罗斯托克大学的合作者。电催化剂有助于电能和化学键的相互转化。这些转变在通过化学燃料储存和提取可再生电力以及合成依赖大量能源投入的大量化学产品方面越来越引起人们的兴趣。高效的催化剂，如自然界中发现的酶，通常依赖于多个化学官能团之间的协同作用来引导反应向所需产品方向发展。这个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，以比单独使用任何一个物种所需的更少的电力输入来驱动反应。工作将集中在合成催化剂上，其中每个介体都连接到一种聚合物上，以便它们保持紧密的接近。虽然将获得的知识从根本上适用于广泛的重要化学物质，但该项目将从模型反应(例如，将简单醇类选择性氧化为醛)发展到涉及更高价值底物的反应。特别是，将使用从生物质中提取的原材料来生产环保的绿色塑料单体化合物。从应用的角度来看，可扩展氧化工艺的发展可能会改变用于化学生产的电解法的经济格局。教育一体化举措将包括将不同的本科生纳入研究进程，并继续开发基于网络的教育单元。与德国罗斯托克大学的国际合作是该项目的关键组成部分，参与该项目的研究生将有机会访问研究。该项目是通过“NSF-DFG在电合成和电催化方面的领导机构活动(NSF-DFG eChem)”机会获得的，这是一个由NSF和德国Forschungsgomeinschaft(DFG)参与的合作征集活动。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。使用均相分子催化剂很难设计出具有多个参与官能团的量身定制的底物结合环境，而使用非均相催化剂材料则更具挑战性。这项提议旨在理解和开发由有机氧化还原介体和氧化还原活性金属中心组成的协同电催化中心，两者都进行电子转移。这项工作借鉴了最近关于均相氧化还原介体机制的演示，其中双电子氧化是通过在两个介体中各提取一个电子来实现的，通过避免较高的介体氧化态来降低必要的应用电位，通常情况下会进入较高的介体氧化态来实现两电子氧化。这种机制从根本上不同于更常见的协作性例子，如金属-配体。合作研究小组寻求发展有效地将这种合作催化剂固定到(A)可溶(但容易分离)聚合物和(B)多相电极上所需的基本认识和方法。这两个平台提供了互补的手段，以确定固定所施加的限制，并了解如何最好地保持合作性。机理研究将被用来了解不同复杂性的探针反应中的电氧化协同性：(I)伯醇选择性地转化为醛；(Ii)5-(羟甲基)-呋喃(HMF)氧化为二甲基呋喃(DFF)(绿色塑料和其他化学应用的单体)，以及(Iii)多电子氧化生成羧酸-特别是HMF生成2，5-呋喃二酸(FDCA)，另一种需要醛和醇基氧化的单体。这些反应对扩大生物质有价化领域至关重要，同时也是了解实现合作性的关键限制因素的信息试验台。这项工作进一步解决了与复杂材料上的电催化活性基准相关的广泛问题，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，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.