Collaborative Research: Photoelectrosynthetic Aminoxyl Catalyzed Alcohol Oxidation

木质纤维生物质提供了一种碳中性的替代燃料和化学品来源，目前这些燃料和化学品来自石油和其他化石燃料。木质素是一种在很大程度上未得到充分利用但化学含量丰富的生物精炼工业副产品，将其转化为有价值的芳香族平台化学品是一个能源密集型过程，使这种方法成本高昂。最近，染料敏化光电合成电池(类似于光伏电池)作为一种将太阳能转化为化学燃料或电能的低成本和环境友好的技术而出现。这些光电化学电池提供了一种在环境温度和压力下使用可再生太阳能来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的光阳极如何在合适的催化剂下化学选择性地氧化木质素，作为迈向完整的光驱动木质素解聚过程的第一步。这一方法将扩大使用多相催化氧化伯醇和仲醇，以生成精细化工和制药工业所需的羰基或羧基化合物。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、会议演示以及为STEM领域未来的专业人员组织和主办教育推广计划向公众传播。专业人员还将通过外展方案积极招募和支持代表性不足的少数族裔学生。有机氧化反应在有机合成或木质纤维素生物质加工中很重要。化学选择性氧化木质素中的脂肪族和/或苯甲醇部分是控制木质素降解以产生所需小分子产物的良好靶标。本项目旨在阐明一种光电合成的化学选择性氧化木质素中的醇部分，通过使用氨基氧基介体和染料敏化光阳极(DSP)相结合的方法。这种方法的关键是使用染料敏化的电极界面通过光诱导电荷分离来激活氮氧基介体。这既提供了一种新的方法来驱动木质素中的仲苄醇和初级脂肪醇官能团的光化学氧化，也为传统上专注于分解太阳能水的染料敏化光电合成电池提供了一种新的光催化应用。该方法将涉及(1)光活性聚合物催化剂的合成及其用于激活氮氧基介体的潜在的光化学电子转移性质的阐明，(2)基于介孔半导体的电极的制备和评价，该电极专为具有一系列氮氧基介体的木素二聚体模型化合物的化学选择氧化而设计，以及(3)利用数字信号处理器(DSP)阐明20-O-苄基和10-脂肪醇的光驱动氧化的机理，并解决使用齐聚物模型化合物和技术木素所带来的实际挑战。作为数字信号处理器在室温下对真实木质素进行选择性氧化的第一个测试案例，这项研究具有重要意义，作为向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。

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.