Nitrogen In the Circular Economy (NICE): The valorisation of nitrogenous waste

项目背景(确定问题及其与可持续性的重要性和相关性)含氮分子无处不在，构成许多基本的农用化学品、药品、添加剂、纺织品和高性能材料的基础。几乎所有含氮分子的合成都需要氨，氨是从哈伯-博世(HB)工艺中衍生出来的。HB过程对环境有很大的不利影响：它消耗了全球约2%的能源，估计占全球二氧化碳排放量的2%。因此，生产含氮化合物的环境成本很高。此外，这些资源被过度消耗，一旦实现了最初的目的，就会被当作废物丢弃。这是我们线性经济的症状；幸运的是，循环经济提供了解决方案。为了从线性经济过渡到循环经济，需要开发能够将废物转化为有用的高价值产品和材料的工艺。富含蛋白质的生物质废物很丰富，但含氮部分仍然被低估和利用。将这种富含蛋白质的废液转化为有用的、高价值的含氮化学品是提高其合成可持续性的一种方法。对未活化的C-N键的化学选择性断开的发展，特别是在未被探索的转化中，将使我们能够从含氮废物中合成小型含氮化合物，从而减少我们对HB工艺的依赖，并降低生产此类化学品的环境成本。建议的解决方案和方法本研究项目致力于开发方法，对资源丰富、目前未得到充分利用的含氮废物流进行定价，并将其转化为精细化学品，而不会扰乱食物链或需要更多作物的生长。通过对不同含氮底物选择性C-N西格玛键断裂的研究，该项目设想开发出使这些废气作价的方法，以改善含氮化合物在氮循环中的流动，并使其能够过渡到更循环的经济。目前技术水平的选择性C-N西格玛键断裂需要令人难以置信的强制条件和/或激活的底物，这限制了这些方法的当前应用。文献中也缺乏机械性的理解，这可能会阻碍新方法的发展。本项目旨在通过开发选择性C-N键断裂的新型催化系统来解决这些问题。将进行催化剂筛选，以寻找能够促进C-N sigma键活化和裂解的催化剂，使用模型N-化合物来探索和比较催化剂的反应性和选择性，根据它们对C-N键裂解的活性、商业可用性、合成简易性和放大潜力进行选择。特别是，第一排过渡金属络合物将因其可持续的资质、低成本和研究小组的专业知识而被优先考虑。在确定合适的催化剂系统后，将进行优化，重点是提供高产品产率和选择性，同时根据绿色化学12原则考虑反应的可持续性。将通过测试具有各种属性的大范围底物来扩大底物范围，以深入了解催化剂系统的局限性。整个项目收集的数据将不断进行分析，以深入了解催化剂的作用机理，包括分离潜在的反应中间体，以及详细的动力学研究；这一见解将使提出一个合理的催化循环成为可能。

Project background (identification of the problem and its importance and relevance to sustainability) Nitrogen containing molecules are ubiquitous and form the basis of many essential agrochemicals, pharmaceuticals, additives, textiles, and performance materials. The synthesis of nearly all nitrogen containing molecules requires ammonia, which is derived from the Haber-Bosch (HB) process. The HB process has a large detrimental environmental impact: it uses around 2% of global energy and contributes an estimated 2% to global carbon dioxide emissions. Consequently, the production of nitrogen containing compounds comes at a high environmental cost. Additionally, these resources are overconsumed and then discarded as waste once their initial purpose has been fulfilled. This is a symptom of our linear economy; fortunately, the circular economy provides a solution. To transition from a linear to a circular economy, processes need to be developed that enable waste to be transformed into useful, high value products and materials. Protein-rich biomass waste streams are abundant, yet the nitrogenous fraction remains undervalued and underused. The valorisation of such protein-rich waste streams into useful, high value, nitrogenous chemicals is one approach to improve the sustainability of their synthesis. The development of chemoselective disconnections for unactivated C-N bonds, particularly in underexplored transformations will enable the synthesis of small nitrogen containing compounds from nitrogenous waste, reducing both our dependence on the HB process and the environmental cost of producing such chemicals. Proposed solution and methodology This research project strives to develop methods to valorise nitrogenous waste streams that are abundant, currently underused, and for which valorisation into fine chemicals will not disrupt the food chain or require the growth of more crops. Through research into selective C-N sigma bond cleavage of various nitrogenous substrates, this project is envisioned to develop methods to valorise these waste streams to improve the flow of nitrogen containing compounds through the nitrogen cycle and to enable the transition towards a more circular economy. The current state of the art for selective C-N sigma bond cleavage requires incredibly forcing conditions and/ or activated substrates which limit the current applications of these methods. There is also a lack of mechanistic understanding in the literature, which can impede the development of novel approaches. This project seeks to address these issues by developing novel catalytic systems for selective C-N bond cleavage. Catalyst screening will be performed to find catalysts which can facilitate C-N sigma bond activation and cleavage using model N-compounds to explore and compare catalyst reactivities and selectivities, selected according to their activity towards C-N bond cleavage, commercial availability, ease of synthesis, and their scale-up potential. In particular, complexes of first row transition metals will be prioritised due to their sustainable credentials, low cost, and research group expertise. Upon the identification of a suitable catalyst system, optimisation will be carried out focusing on delivering high product yield and selectivity, whilst considering reaction sustainability in accordance with the 12 Principles of Green Chemistry. Substrate scope will be expanded by testing a large range of substrates with a variety of properties to gain insight into the limitations of the catalyst system. Data collected throughout this project will be continually analysed to gain insight into the catalyst mechanism of action, including isolation of potential reaction intermediates, along with detailed kinetic investigations; together this insight will enable a plausible catalytic cycle to be proposed.