Collaborative Research: Photoelectrosynthetic Aminoxyl Catalyzed Alcohol Oxidation

木质纤维素生物质为目前依赖石油和其他化石燃料的燃料和化学品提供了一种碳中性的替代来源。将木质素转化为有价值的芳香平台化学品是一个能源密集型的过程，这使得这种方法的成本过高。木质素是生物精炼工业的一种很大程度上未被充分利用但化学成分丰富的副产品。最近，染料敏化光电合成电池（类似于光伏电池）作为一种低成本和环境友好的技术出现，将太阳能转化为化学燃料或电力。这些光电化学电池提供了一种利用可再生太阳能在环境温度和压力下驱动能源密集型化学转化的方法。在这里，合作的基础研究项目将研究染料敏化光阳极如何用合适的催化剂化学选择性氧化木质素，作为实现完整的光驱动木质素解聚过程的第一步。这种方法将扩大使用多相催化氧化伯醇和仲醇，为精细化工和制药工业生产羰基或羧基化合物。这项工作代表了染料敏化光电合成电池的新应用，该项目的研究成果将通过研究出版物、会议报告、组织和主持STEM领域未来专业人员的教育推广计划向公众传播。私立学校还将通过外展计划积极招收和支持代表性不足的少数民族学生。有机氧化反应在有机合成或木质纤维素生物质加工中具有重要意义。化学选择性氧化木质素中的脂肪族和/或苯基醇部分是控制木质素降解以产生所需小分子产物的一个很好的目标。本项目旨在通过在室温下结合使用氨基氧基介质和染料敏化光阳极（DSP）来阐明木质素中醇部分的光电合成化学选择性氧化。这种方法的关键是使用染料敏化电极界面通过光诱导电荷分离来激活硝基介质。这为木质素中发现的仲苯醇和伯脂肪醇官能团的光化学氧化提供了新的途径，也为染料敏化光电合成电池提供了新的光催化应用，而传统上染料敏化光电合成电池主要集中在太阳能水分解上。该方法将涉及(1)光活性聚合物催化剂的合成和阐明其激活硝基介质的潜在光化学电子转移性质，(2)制造和评估介孔半导体电极，专门设计用于木质素二聚体模型化合物与一系列硝基介质的化学选择性氧化。(3)阐明了利用DSP光驱动氧化20苯基和10脂肪醇的机制途径，并解决了使用低聚物模型化合物和技术木质素所带来的实际挑战。这项研究具有重要意义，因为它是DSP的第一个测试案例，可以在室温下对真正的木质素进行选择性氧化，作为将光驱动生物质转化为增值化学品的第一步。该奖项反映了美国国家科学基金会的法定使命，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。

Lignocellulosic biomass offers a carbon-neutral alternative source of fuels and chemicals which are currently sourced from petroleum and other fossil fuels. Converting lignin, a largely underutilized yet chemically rich byproduct of the biorefining industry, to valuable aromatic platform chemicals is an energy-intensive process that has made this approach cost prohibitive. Recently, dye-sensitized photoelectrosynthetic cells (similar to photovoltaic cells) have emerged as a low-cost and environmentally friendly technology for converting solar energy into chemical fuels or electricity. These photoelectrochemical cells offer a means of using renewable solar energy to drive energy-intensive chemical conversions at ambient temperature and pressure. Here, the collaborative fundamental research project will study how a dye-sensitized photoanode can chemoselectively oxidize lignin with a suitable catalyst as a first step toward a complete light-driven lignin depolymerization process. This approach will expand on the use of heterogeneous catalysis for the oxidation of primary and secondary alcohols to produce carbonyl or carboxyl compounds for the fine chemical and pharmaceutical industries. This work represents a new application for dye-sensitized photoelectrosynthetic cells, and the research findings from the project will be disseminated to the public through research publications, conference presentations, and by organizing and hosting educational outreach programs for future professionals in the STEM field. The PIs will also actively recruit and support underrepresented minority students through the outreach program.Organic oxidation reactions are important in organic synthesis or lignocellulosic biomass processing. Chemoselective oxidation of the aliphatic and/or benzylic alcohol moieties in lignin is a good target for controlling the degradation of lignin to generate desired small molecular products. This project aims to elucidate a photoelectrosynthetic chemoselective oxidation of alcohol moieties in lignin by combining the use of aminoxyl mediators with a dye-sensitized photoanode (DSP) at room temperature. Essential to this approach is the use of a dye-sensitized electrode interface to activate a nitroxyl mediator via light-induced charge separation. This presents both a new approach for driving the photochemical oxidation of the secondary benzylic alcohol and the primary aliphatic alcohol functional groups found in lignin, as well as a new photocatalytic application for dye-sensitized photoelectrosynthetic cells, which have traditionally focused on solar water splitting. The approach will involve (1) the synthesis of photoactive polymeric catalysts and the elucidation of their underlying photochemical electron transfer properties for activating nitroxyl mediators, (2) the fabrication and evaluation of mesoporous semiconductor-based electrodes specifically designed for the chemoselective oxidation of lignin dimer model compounds with a series of nitroxyl mediators, and (3) the elucidation of mechanistic pathways for the light-driven oxidation of 2o benzylic and 1o aliphatic alcohols using a DSP and address practical challenges presented by the use of oligomer model compounds and technical lignin. This research is significant as a first test case of a DSP to carry out the selective oxidation of real lignin at room temperature as a first step toward light-driven biomass conversion to value-added chemicals.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.