Heterogeneous catalysis is widely exploited by the chemical industry, both in batch reactors and in continuous flow, the latter via the use of packed bed reactors. Unfortunately, the transfer of commercially available heterogeneous catalysts to high pressure flow systems is often difficult, with challenges such as catalyst deactivation through metal leaching, and the crushing of pelleted supports. Thus, the limited availability of suitable catalysts for heterogeneous flow processes, which can satisfy all the requirements for its application, is a major bottle neck in the commercial implementation of these systems. Polymer-based spherical activated carbon beads (diameter = 474 ± 96 μm) offer a promising solution: these small, spherical and monodisperse beads have high mechanical strengths and large surface areas (1583 ± 8 m² g⁻¹), offering desirable properties for this task, such as reproducible packing and low pressure drops across packed catalyst beds. Two series of Pd/C spherical bead catalysts were synthesised and compared to a commercial catalyst from Johnson Matthey (1 wt% Pd/C pellets), in small scale screenings (20 mg) via a recirculating batch platform, for their activity in a model nitro reduction reaction. It was observed that small, robust, highly active palladium nanoparticles (PdNPs) supported on spherical carbon beads with a narrow size distribution (e.g. 1e – Pd – d_NP = 5.0 ± 1.4 nm) can be synthesised via solution phase deposition. In contrast, the NP catalysts made via gas phase deposition were much larger (e.g. 2e – Pd – d_NP = 22.8 ± 13.1 nm), less active and unstable due to metal leaching. The applicability of these NP catalysts for use in continuous flow was subsequently demonstrated on a larger scale (0.5–1 g), with a high activity and stability achieved over a two day operating period. This work demonstrates the production of an active, stable heterogeneous catalyst suitable to be employed in a pilot scale continuous flow packed bed reactor, for the production of APIs.

中文翻译：

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钯纳米粒子沉积在球形碳载体上用于连续流中的多相催化

多相催化在化学工业中得到了广泛的应用，无论是在间歇式反应器还是在连续流中，后者通过使用填充床反应器。不幸的是，将市售的非均相催化剂转移到高压流动系统通常很困难，面临诸如金属浸出导致催化剂失活以及颗粒载体破碎等挑战。因此，能够满足其应用的所有要求的用于非均相流过程的合适催化剂的可用性有限，是这些系统商业实施的主要瓶颈。基于聚合物的球形活性炭珠（直径= 474 ± 96 μm）提供了一个有前途的解决方案：这些小型球形单分散珠具有高机械强度和大表面积（1583 ± 8 m ² g ^-1），为这项任务，例如可重复的填充和填充催化剂床的低压降。合成了两个系列的 Pd/C 球形珠催化剂，并通过循环批次平台小规模筛选（20 毫克）与 Johnson Matthey 的商用催化剂（1 wt% Pd/C 颗粒）进行比较，以了解其在模型中的活性硝基还原反应。据观察，可以通过溶液相沉积合成负载在具有窄尺寸分布（例如 1e – Pd – d _NP = 5.0 ± 1.4 nm）的球形碳珠上的小而坚固的高活性钯纳米颗粒（PdNP） 。相比之下，通过气相沉积制备的NP催化剂要大得多（例如2e – Pd – d _NP = 22.8 ± 13.1 nm），活性较低且由于金属浸出而不稳定。随后在更大规模（0.5-1 g）上证明了这些 NP 催化剂在连续流动中的适用性，并在两天的运行期内实现了高活性和稳定性。这项工作展示了一种活性、稳定的多相催化剂的生产，适用于中试规模的连续流动填充床反应器，用于生产 API。