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

项目背景（识别问题及其重要性和与可持续性的相关性）含氮分子无处不在，是许多基本农用化学品、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，氨来自哈伯-博施（HB）工艺。HB工艺对环境有很大的不利影响：它使用了全球约2%的能源，估计占全球二氧化碳排放量的2%。因此，含氮化合物的生产以高的环境成本为代价。此外，这些资源被过度消耗，一旦达到最初的目的，就被当作废物丢弃。这是我们线性经济的一个症状;幸运的是，循环经济提供了一个解决方案。 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流很丰富，但含氮部分仍然被低估和利用不足。将这种富含蛋白质的废物流转化为有用的、高价值的含氮化学品是提高其合成的可持续性的一种方法。 未活化的C-N键的化学选择性断开的发展，特别是在未充分探索的转化中，将使得能够从含氮废物合成小的含氮化合物，减少我们对HB过程的依赖和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，以稳定目前未充分利用的大量含氮废物流，并且稳定为精细化学品不会破坏食物链或需要更多作物的生长。通过对各种含氮基质的选择性C-N σ键断裂的研究，该项目设想开发方法来评价这些废物流，以改善含氮化合物通过氮循环的流动，并使其向更循环的经济过渡。 用于选择性C-N σ键断裂的现有技术需要令人难以置信的强制条件和/或活化的底物，这限制了这些方法的当前应用。在文献中也缺乏机械的理解，这可能会阻碍新方法的发展。该项目旨在通过开发用于选择性C-N键断裂的新型催化体系来解决这些问题。 将进行催化剂筛选以发现可以使用模型N-化合物促进C-N σ键活化和裂解的催化剂，以探索和比较催化剂反应性和选择性，根据它们对C-N键裂解的活性、商业可用性、合成的容易性和它们的放大潜力进行选择。特别是，第一行过渡金属的络合物将优先考虑，因为它们具有可持续性、低成本和研究小组的专业知识。在确定合适的催化剂系统后，将进行优化，重点是提供高的产品收率和选择性，同时根据绿色化学的12项原则考虑反应的可持续性。基质范围将通过测试具有各种性质的大范围基质来扩展，以深入了解催化剂系统的局限性。将持续分析在整个项目中收集的数据，以深入了解催化剂的作用机制，包括分离潜在的反应中间体，沿着详细的动力学研究;这些见解将共同促成提出合理的催化循环。

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.