Metal Nanoclusters as Heterogeneous Catalysts in Flow Reactors

金属纳米团簇(MNC)是指直径小于2.0 nm的金属原子团簇，可以由单一或多个金属组成。跨国公司显示出作为多相催化剂的前景，团簇被沉积在载体上或被包裹起来。这些催化剂实现了传统均相催化剂的高比表面积，表现出高活性和高选择性，同时保持了多相催化剂的稳定性和易分离性。这样的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，这对稀有或昂贵的金属是有利的，从可持续性的角度来看也是非常可取的。到目前为止，MNC的合成通常采用湿化学法，这种方法需要多个步骤，会产生废物，而且不能规模化，阻碍了商业应用。可以克服这些问题的一种制备技术是磁控溅射。这种物理过程可以在单一步骤中将平面金属团簇直接分散到载体上，并对金属负载和团簇大小进行高水平的控制。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更加重要。磁控溅射的使用还将使MNC多相催化剂的生产规模和产量不会限制他们的研究。与此同时，流动中的多相催化是一个不断发展的领域，在改进现有的化学过程以及开发新的和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、传热和控制反应混合物的流动方面有局限性。因此，许多新型的反应堆系统被开发出来，如3D打印插件和涡流装置。在该项目中，这两种新兴的可持续发展技术将被连接在一起；通过磁控溅射制备MNC，然后用作液体流动中的非均相催化剂。就我们所知，MNC催化剂还没有在液体流动中被证明，也不知道哪种流动反应器方法将最好地利用它们的独特性质。这是一个具有挑战性的问题，因为不同的流动反应堆技术对MNC制造的具体要求是不同的。该项目旨在确定MNC催化剂在流动中的行为和性能，这对可持续使用过渡金属用于流动过程的多相催化的工业挑战至关重要。为了实现这一步骤的改变，需要采取多学科的方法。多相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。将对反应结果进行分析，包括产品转化率、产品纯度和反应速率，以了解催化剂的性能。在不同的流动反应器中进行反应将有助于了解不同的载体类型和反应条件如何影响这种行为和性能。首先，将以氢化反应为模型反应来研究钯MNCs。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多相液体流动催化剂，具有在重要工业反应中应用的潜力。

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.