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Publication date: 8 January 2022

Source: Tetrahedron, Volume 104

Author(s): Alessandro Sacchetti, Carolina Urra Mancilla, Greta Colombo Dugoni

Nature, Published online: 22 November 2021; doi:10.1038/d41586-021-03447-w

Our study demonstrates a seamless scale-up of photochemical C−C-cross-couplings of aryls and alkyls via dual Ir/Ni photoredox catalysis. The herein described novel type of internal illumination using wirelessly powered LEDs inside the reaction media allows for efficient scaling and intensification of those reactions, maintaining virtually identical reaction profiles over all scales. The system is readily applicable to other light-driven reactions as well.

Abstract

Carbon−carbon bond formation by dual Iridium-Nickel photoredox catalysis has gained a lot of attention for late-stage cross-couplings of alkyls with aryls. However, the scalability of such reactions is greatly impeded by the poor light penetration depth into the strongly absorbing reaction media. Wireless internal illumination is a novel technique which circumvents the light penetration issue efficiently and therefore allows to scale photon-driven reactions by conventional methods. Here we demonstrate that industrially relevant photoredox C−C couplings can be scaled seamlessly to different volumes, achieving qualitatively and quantitatively the same results at all scales. The use of conventional reactor types allows stirred, bubble column or fixed-bed operation mode and is fully compatible with heterogeneous reaction mixtures. By minimizing reflection losses, we could also show a significant advantage in the reaction rate over an externally illuminated setup at the same light intensity.

The Cover Feature shows a representative native structure of lignin with several minor units. When the structure is reductively cleaved into aromatic monomers the focus is normally on the products on the right-hand side as these are the main products. However, the monomers shown on the left-hand side can also become a significant part of the product mixture depending on the parent lignin structure. Detailed analysis of the product mixture and the structure of the lignin can reveal the origin of these minor products. More information can be found in the Full Paper by Z. Wang and P. J. Deuss.

Single-atom Catalysis: This review shows the research progress to increase the density of active sites in single-atom catalysts (SACs) from the pioneer work with metal loading below 0.2 wt% to the recently-reported works with metal loading above 20 wt%. The successful preparation strategies to achieve high metal-loading SACs are highlighted, and the perspectives to further improve the quality of high metal-loading SACs are pointed out.

Abstract

Although single-atom catalysts (SACs) show significantly higher catalytic performance compared to conventional and nanoparticle-based catalysts (NPs) at the same amount of metal loading, their overall catalytic performance may still be unable to compete with the NPs in many applications due to the limited active sites. Generally, trace amounts of metal (less than 1 wt%) can be successfully loaded onto supports in an atomically-dispersed feature, and higher metal loading usually results in aggregation of the metal atoms. Hence, it is very important to further increase the density of isolated metal atoms in these rising-star SACs to pave the ways for widespread applications or even to replace the NPs. On the other hand, it is well known that this is one of the most challenging topics on SACs research. In this review, the advanced strategies to overcome this challenge and achieve high loading of isolated metal atoms on various supports will be extensively discussed together with the examples showing the research efforts to enrich the metal active sites from the pioneer works with metal loading below 0.2 wt% to the recently-reported SACs with metal loading over 20 wt%. Besides, there are still plenty of rooms to further improve the quantity and quality of metal loading on different supports, and outlooks of this scope is provided. We hope that this comprehensive review aids in the development of synthesis techniques for the new-generation SACs with richer active sites.

Nature, Published online: 26 October 2021; doi:10.1038/d41586-021-02906-8