An iridium catalyst for the base-free dehydrogenation of neat formic acid

Significance 

Increasing strict measures on carbon emissions has highly favored the development of low-carbon technologies-based energy sources. Among the available renewable energy sources, hydrogen has the great potential to reduce carbon emission in both mobile and distributed energy applications. Unfortunately, deploying hydrogen as a clean energy source has been hindered by several challenges among them being hydrogen storage and large-scale utilization.

Recently chemical storage of hydrogen has been developed in the form of formic acid and now considered a promising solution for stationary hydrogen storage due to its stability and less hazardous issues. In particular, the dehydrogenation of formic acid has been given special attention.

Several heterogeneous and homogeneous catalysts for formic acid dehydrogenation have been explored. However, due to their low activity some of these catalysts are not suitable for dehydrogenation of formic acid while more efficient catalysts require base additives and/or diluted conditions hence hampering their practical implementation. Alternatively, iridium-based homogeneous catalysts have been developed for this purpose. Generally, they can efficiently operate in water and have a high potential application as compared to other homogeneous catalysts. On the other hand, base-free conditions for the dehydrogenation of pure and aqueous formic acid are required to enhance the interest of this catalytic process. Unfortunately, this area has not been fully explored.

To this note, researchers at University of Rennes: Shengdong Wang, Haiyun Huang, Dr. Christian Bruneau, Dr. Thierry Roisnel (X-ray Crystallographer) and Dr. Cédric Fischmeister synthesized iridium catalysts for base-free dehydrogenation of pure formic acid. The research team intended to contribute to the world of knowledge about dehydrogenation of aqueous and neat formic acid for use in hydrogen energy generation. Their research work is currently published in the research journal, ChemSusChem.

In brief, the research team synthesized electron-rich iridium(III)Cp*(dipyridylamine) catalysts and cross-examined base-free conditions suitable for aqueous and neat formic acid dehydrogenation. Additional consideration was taken to detect the presence of any carbon monoxide during the catalysis process that would prevent potential application in fuel-cells. Additionally, considering the high stability of the catalysts, its latent behavior and potential for semi-continuous mode application was investigated.

The authors observed that the electron-enriched catalysts were suitable for efficient dehydrogenation of both aqueous and neat formic acid in base-free conditions. This was attributed to high stability of the catalyst under acidic conditions and to hydrogen-bonding assisted formic acid activation. For instance, TOF of 13292 h-1 was reported at a temperature of 100 °C for the dehydrogenation of neat formic acid. Furthermore, the iridium(III) complexes exhibited latent behavior with potential practical applications and the reaction did not generate undesired CO (below 1 ppm).

In summary, the University of Rennes scientists successfully demonstrated dehydrogenation of both aqueous and neat formic acid using iridium complex catalysts which are considered to be among the most efficient catalysts. Altogether, the study will advance exploration and generation of hydrogen energy as an alternative source of renewable energy. Also, it will pave the way for investigation of the catalytic mechanism to unleash their full potential.

An iridium catalyst for the base-free dehydrogenation of neat formic acid - Advances in Engineering

About the author

Dr. Shengdong Wang received his MSc from Chemistry & Environment Science College, Inner Mongolia Normal University, China and followed a Student Exchange program at the Institute of Chemistry, Chinese Academy of Sciences Beijing, working under the supervision of Prof. Wen-Hua Sun. From 2015 to 2018 he was a doctorate student at the University of Rennes where he worked on the catalytic valorization of platform chemicals such as levulinic acid and formic acid dehydrogenation under the supervision of Dr. Cédric Fischmeister.

He is currently a post-doc researcher at the Institut de Chimie Moléculaire et des Matériaux d’Orsay, Université Paris-Sud, France, working on use of alkaline earth metal complexes as catalysts for C–O bond functionalization in the group of Prof. Vincent Gandon.

About the author

Ms Haiyun Huang received her BsC from Guangdong University of Education, Guangzhou, China and her MSc from the University of Rennes, France where she has been working on transition metal-catalyzed valorization of renewables and hydrogen production under the supervision of Dr. Cédric Fischmeister.

She is currently pursuing a PhD at the University of Rennes under the supervision of Dr. Henri Doucet working on palladium-catalyzed C-H bond functionalization.

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About the author

Dr. C. Bruneau graduated in chemistry from the Institut National Supérieur de Chimie Industrielle de Rouen (France, 1974) and got his PhD at the University of Rennes (1979). He obtained a CNRS position in 1980 and since 1986 has been working in the field of transition metal catalysis at the University of Rennes.

He has been mainly involved in ruthenium and recently iridium-catalyzed selective transformations (olefin metathesis, allylation, sp2 and sp3 C-H bond activation and functionalization, hydrogen transfer, asymmetric catalysis, additions to alkynes, bio resources transformations). From 2000 to 2011, he was the head of the CNRS–University of Rennes research group “Organometallics and Catalysis”.

He is the recipient of the prize of the Coordination Chemistry Division (2008) and Le Bel prize (2016) from the French Chemical Society, and Paul Langevin prize (2012) from the French Academy of Sciences.

About the author

Dr. Cédric Fischmeister received his PhD degree in 1998 from the University of Montpellier II working on the synthesis of hybrid organic-inorganic materials under the supervision of Profs. Robert Corriu and Geneviève Cerveau. He then joined the group of Prof. Régis Réau in Rennes to work on phosphole-containing conjugated molecules for light emitting materials. After spending 16 months as a post-doc research associate in the group of Prof. Andrew Holmes at the Melville Laboratory for polymer synthesis in Cambridge UK, working on the synthesis of PPVs for LEDs, he was appointed in 2001 as a CNRS research engineer in the group of Dr. Christian Bruneau and Prof. Pierre Dixneuf, and obtained the “Habilitation à Diriger des Recherches” in 2008.

His research interests concern organometallic chemistry and homogeneous catalysis applied to the transformation and valorization of renewable materials using essentially olefin metathesis and reduction transformations. He is also interested in future energy carriers such as hydrogen and in the implementation of sustainable chemical transformations and processes.

Reference

Wang, S., Huang, H., Roisnel, T., Bruneau, C., & Fischmeister, C. (2019). Base-Free Dehydrogenation of Aqueous and Neat Formic Acid with Iridium (III) Cp*(dipyridyl amine) Catalysts. ChemSusChem, 12(1), 179-184.

Go To ChemSusChem

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