Metal Nanoclusters as Heterogeneous Catalysts in Flow Reactors

金属纳米团簇（MNCs）是直径小于2.0 nm的金属原子团簇，可以由单个或多个金属组成。MNCs表现出作为多相催化剂的潜力，其中簇沉积在载体上或被封装。这些催化剂实现了传统均相催化剂的高表面积，具有高活性和选择性，同时保留了多相催化剂的稳定性和易于分离性。这种特性可以实现使用纳米颗粒或单原子催化剂无法实现的性能。MNC催化剂还大大减少了催化所需的金属量，这有利于稀有或昂贵的金属，从可持续发展的角度来看是非常可取的。迄今为止，MNCs通常使用湿化学方法合成，这需要多个步骤，产生废物并且不可扩展，阻碍了商业应用。一种可以克服这些问题的制备技术是磁控溅射。这种物理过程可以在一个步骤中将平面金属团簇直接分散到支架上，并对金属负载和簇大小进行高度控制。与湿化学方法不同，该过程不会产生任何化学废物，这一点至关重要，因为减少化学研究对环境的影响变得越来越重要。磁控溅射的使用也将使MNC异相催化剂能够以不限制其研究的规模和吞吐量产生。与此同时，流动中的多相催化是一个不断发展的领域，在改进现有化学工艺以及开发新的、更可持续的化学方面具有巨大的潜力。通常使用填充床反应器，但是这些反应器在混合、传热和对反应混合物流动的控制方面有局限性。因此，许多新型反应器系统已经被开发出来，如3d打印的插入和涡流装置。在这个项目中，两种新兴的可持续技术将结合在一起；采用磁控溅射法制备MNCs，并将其用作液体流动中的非均相催化剂。据我们所知，MNC催化剂尚未在液体流动中得到证明，也不知道哪种流动反应器方法能最好地利用其独特的性质。这是一个具有挑战性的问题，因为不同流动反应器技术的MNC制造细节将有所不同。该项目旨在建立MNC催化剂在流动中的行为和性能，这对于可持续利用过渡金属进行流动过程多相催化的工业挑战至关重要。要实现这一步骤的变化，需要多学科的方法。异相MNC催化剂系统将通过成像和光谱来表征，以了解它们的行为。反应输出包括产品转化率，产品纯度和反应速率将进行分析，以了解催化剂的性能。在各种流动反应器中进行反应将有助于了解不同的支撑类型和反应条件如何影响这种行为和性能。首先，钯跨国公司将以加氢作为模型反应进行研究。到项目结束时，我们的目标是开发出新一代高性能和可持续的液体流动多相催化剂，具有应用于工业重要反应的潜力。

Metal nanoclusters (MNCs) are metal atom clusters with diameters smaller than 2.0 nm, and can be composed of a single or multiple metals. MNCs show promise as heterogeneous catalysts, where the clusters are deposited on a support or encapsulated. These catalysts achieve the high surface area of traditional homogeneous catalysts exhibiting high activity and selectivity, whilst retaining the stability and separation ease of heterogeneous catalysts. Such characteristics can enable performance that is not achievable using nanoparticle or single atom catalysts. MNC catalysts also drastically reduce the amount of metal required for catalysis which is beneficial for rare or expensive metals and highly desirable from a sustainability perspective. To date, MNCs have generally been synthesised using wet chemistry methods which require multiple steps, produce waste and are not scalable, preventing commercial application. One preparation technique that can overcome these issues is magnetron sputtering. This physical process can disperse planar metal clusters directly onto supports in a single step, with a high level of control over metal loading and cluster size. Unlike wet chemistry methods, the process does not produce any chemical waste which is crucial as it becomes more important to reduce the impact of chemical research on the environment. The use of magnetron sputtering will also enable MNC heterogeneous catalysts to be generated at a scale and throughput that does not limit their research. In parallel to this, heterogeneous catalysis in flow is a growing field and presents huge potential to improve existing chemical processes as well as develop new and more sustainable chemistry. Commonly, packed bed reactors are used, however these can have limitations with respect to mixing, heat transfer and control over the flow of the reaction mixture. As a result, many novel reactor systems have been developed such as 3D-printed inserts and vortex devices. Proposed solution and methodology In this project, the two emerging sustainable technologies will be bridged together; MNCs will be fabricated by magnetron sputtering, and then used as heterogeneous catalysts in liquid flow. To the best of our knowledge, MNC catalysts have not yet been demonstrated in liquid flow, and it is not known which flow reactor approach would be best to harness their unique properties. This is a challenging question because specifics of MNC fabrication will be different for different flow reactor technologies. This project is set to establish MNC catalyst behaviour and performance in flow which is critically important for industrial challenges related to the sustainable use of transition metals for heterogeneous catalysis of flow processes. To achieve this step change a multidisciplinary approach is required. Heterogeneous MNC catalyst systems will be characterised through imaging and spectroscopy to understand their behaviour. Reaction outputs including product conversion, product purity and reaction rate will be analysed to understand catalyst performance. Carrying out the reactions in a variety of flow reactors will help to understand how different support types and reaction conditions impact this behaviour and performance. Initially, Palladium MNCs will be investigated with hydrogenation as a model reaction. By the end of the project we aim to have developed a new generation of high performing and sustainable heterogeneous catalysts for liquid flow with potential for application to industrially important reactions.