Fine-tuning ruthenium nanoparticles with 2,2'-Bipyridine: Size vs. performance Álvaro Lozano-Roche 1 , Nuria Romero 2 , Laia Francàs 1 , Karine Philippot 2 , Jordi García-Antón 1 , Xavier Sala 1 1 Unviersitat Autònoma de Barcelona, Spain, 2 Laboratoire de Chimie de Coordination, France In recent years metallic nanoparticles (NPs) have increased their popularity for numerous catalytic applications. This is largely due to their size-related properties. When compared to typical homo- and heterogeneous catalysts, metallic NPs gather some of the best properties of both worlds such as a large number of active sites and enhanced stability, while also displaying a certain degree of tuneability. [1] One particularly interesting method for the synthesis of metallic NPs is the organometallic approach. This procedure entails the controlled decomposition of an organometallic precursor in the presence of a stabiliser, usually a ligand of interest, under mild conditions. In this way, the synthesised NPs present a clean surface free of contaminant by-products. [2] Interestingly, these ligands can have an effect on the physicochemical properties of the NPs. The presence of certain species on the surface of the NPs can be used to control their size and tune their active sites, enhancing their catalytic performance. [3] One good example can be found in Ru NPs stabilised with 4-phenylpyridine (4PP). Our group showed that the presence of the 4PP ligand on these NPs shifts the Ru-H bond energy to an optimal value, therefore increasing their catalytic performance towards the hydrogen evolution reaction (HER). [3] Inspired by this work, we decided to test the effect of 2,2’-bipyridine (bpy) on Ru NPs. Herein we present various systems consisting of Ru NPs stabilised with different amounts of bpy. It was found that there is an inverse relationship between the amount of bpy used and the size of the resulting nanoparticles i.e. , the more equivalents of ligand added, the smaller the nanoparticles and vice versa. These differences in size also translate into large differences in their catalytic performances towards HER being the smallest system the worst catalyst and the biggest one the best. This behaviour can seem counterintuitive, although it can be justified by the coordination of the bpy ligand on the surface of the NPs and its effect on the active sites of these catalysts.
References 1. P. Serp, K. Philippot in Nanomaterials in Catalysis (Eds. P. Serp, K. Philippot), Wiley-VCH, Weinheim 2013 , 1-54. 2. C. Amiens, D. Ciuculescu-Pradines, K. Philippot, Coordination Chemistry Reviews 2016 , 308, 409-432. 3. G. Martí et. al. , Adv. Energ. Mater. 2023 , DOI: 10.1002/aenm.202300282. 4. J. Creus, S. Drouet, S. Suriñach, P. Lecante, V. Collière, R. Poteau, K. Philippot, J. García-Antón, X. Sala, ACS Catal. 2018 , 8, 12, 11094-11102.
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