Affordable and Clean Energy (SDG 7), Responsible Consumption and Production (SDG 12)
Hydrogen production from formic acid mediated by molecular Ru(II) catalysts: catalytic performance and mechanistic insights Cassiem Joseph a,b , Rotondwa Mphephub and Andrew Swarts b a Department of Chemistry and Polymer Science, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa, E-mail: cjoseph@sun.ac.za. b Molecular Sciences Institute: School of Chemistry, University of the Witwatersrand, Johannesburg, South Africa The quest for sustainable energy solutions is steering the global research community towards innovations that can revolutionize the way we store and utilize energy. Among the many options, H 2 presents a highly promising path due to its potential for high energy yield and environmental friendliness. [1] However, the broad adoption of H 2 as an energy carrier is hindered by challenges associated with its storage and release. Compressed and cryogenic liquid H 2 storage methods pose economic and safety concerns. They require materials and infrastructure capable of withstanding extreme pressures and temperatures, which translates to high energy and material costs. Formic acid dehydrogenation processes are pivotal in the development of H 2 storage and release systems, offering a promising route for the on-demand production of H 2 gas, a clean energy carrier. [2-3] Formic acid, being a liquid at ambient conditions, serves as a convenient H 2 storage material due to its high hydrogen content and ability to release H 2 through dehydrogenation. The dehydrogenation of formic acid can be catalytically driven under mild conditions, which is advantageous for portable applications and where immediate hydrogen generation is required. Technological advancements in catalyst design and reaction engineering aim to optimize the efficiency, control, and safety of the dehydrogenation reactions, thereby enhancing the practicality of using formic acid in hydrogen storage systems. In light of this, we report on a series of pyridine-pyrazolyl Ru(II) complexes bearing different electronic and steric properties as catalysts for formic acid dehydrogenation (Figure 1). We demonstrated that the catalysts could dehydrogenate formic acid to CO 2 and H 2 in quantitative yields within 1 hour (5mmol FA, 5umol catalyst loading, 3mmol HCOOK, 100˚C) with TON’s and TOF’s of ~1030 molFA dehydrogenated/molcatalyst and ~1230 h-1 achieved respectively. Mechanistic studies for formic acid dehydrogenation are also reported.
Figure 1: Formic acid dehydrogenation catalysed by Ru(II) pyridine-pyrazolyl complexes
Key words: ruthenium catalysts, formic acid dehydrogenation, mechanistic studies References 1. Monney, A.; Barsch, E.; Sponholz, P.; Junge, H.; Ludwig, R.; Beller, M., Chem. Commun ., 2014, 50, 707. 2. Alberico, E.; Sponholz, P.; Cordes, C.; Nielsen, M.; Drexler, H. J.; Baumann, W.; Junge, H.; Beller, M., Angew. Chem. Int. Ed ., 2013, 52, 14162. 3. Léval, A.; Agapova, A.; Steinlechner, C.; Alberico, E.; Junge H.; Bellor M., Green Chem. , 2020, 22, 913.
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