“Selectivity control in hydrogenation through adaptive catalysis using ruthenium nanoparticles on a CO2-responsive support”
Chemical transformations with molecular hydrogen (H2) are fundamental pillars of the chemical industry and used across the whole value chain ranging from the production of fuels, fine chemicals, agrochemicals, and pharmaceuticals. With the rise of alternative renewable energy sources and chemical feedstocks, the permanent evolution of novel hydrogen technologies is of ever increasing importance. Catalysts are essential to control the activation and transfer of hydrogen in particular for the selective conversion of biomass-derived substrates and intermediates. In a world where flexibility is becoming increasingly important, the design and development of such catalysts whose reactivity can be changed at will or even self-adjusts during the process is of great interest, but remains a challenge. In an article recently published in Nature Chemistry, an international team of scientists lead by Prof. Walter Leitner, Director at the Max Planck Institute for Chemical Energy Conversion, now reports a rationally designed catalyst that adapts fully reversibly and in real time to changes in the reaction system, enabling the selective generation of different products depending on the source of hydrogen.
While previously developed catalysts present often outstanding properties regarding their dedicated tasks, their performance is typically optimized to remain static. The development of an adaptive catalytic system - referring here to a catalytic system whose reactivity is reversibly modified upon changes in the reactive environment - is particularly difficult. To tackle this challenge, the research team combined expertise on nanoparticle-based catalysis (Alexis Bordet, Sami El Sayed and colleagues from MPI CEC and RWTH Aachen University) and CO2-responsive materials (Philip G. Jessop's group, Queen's University). When used in the hydrogenation reaction reactions that can lead to different products, the new catalyst is able to “recognize” whether the feed gas is composed of pure hydrogen or a mixture of hydrogen and carbon dioxide (CO2). Depending only on the gas supply, it operates in two different modes producing selectively two different products from the same starting material under otherwise identical conditions. The two modes of operation can be switched back and forth almost in real time.
"Our aim was to develop a catalytic system capable of adapting its reactivity, and in particular selectivity, to its environment in a fully controllable and reversible manner. The catalyst can automatically change its performance just like a chameleon would change its color” explains Dr. Alexis Bordet, group leader at MPI CEC in Prof. Walter Leitner's department.
This study and international cooperation was supported in particular by the Cluster of Excellence “The Fuel Science Center" which has set the development of adaptive catalytic systems as one of its main objectives. The authors hope that their proof of concept of an adaptive catalytic system for hydrogenation reactions will open many new opportunities to develop other adaptive catalytic systems and enable flexible production schemes on basis of renewable feedstock and energy supply.
The scientists have prepared a multifunctional hydrogenation catalyst composed of ruthenium nanoparticles immobilized on an amine-functionalized support, and applied it to the hydrogenation of a biomass-derived molecule, furfuralacetone. When the hydrogenation was performed under a pressure of pure hydrogen (H2), furfuralacetone was completely hydrogenated to give the corresponding saturated alcohol. However, when a mixture of H2 and carbon dioxide (CO2) was used, a sharp change in selectivity was observed, where the furan ring and the double bond were still efficiently hydrogenated while the ketone was conserved.
The change in selectivity – which was not observed for a reference Ru@SiO2 – is presumably due to the formation of an alkylammonium formate species coming from the reaction between the amine functionality, CO2 and H2. This process is reversible, allowing switching the feed gas composition back and forth between H2 and CO2 + H2 in continuous flow reactor to produce either the saturated alcohol or the saturated ketone in excellent selectivities and yields.
Future studies will aim at getting a deeper understanding of the switching mechanism in order to expand the scope of accessible substrates and reactions, and pave the road toward the development of new adaptive catalytic systems with tailor-made reactivity.
Original Paper: Bordet, A., El Sayed, S., Sanger, M., Boniface, K. J., Kalsi, D., Luska, K. L., Jessop, P. G., Leitner, W. Selectivity control in hydrogenation through adaptive catalysis using ruthenium nanoparticles on a CO2-responsive support. Nat. Chem. (2021). https://doi.org/10.1038/s41557-021-00735-w
For further information on the design of multifunctional catalysts: Bordet, A., Leitner, W. Metal Nanoparticles Immobilized on Molecularly Modified Surfaces: Versatile Catalytic Systems for Controlled Hydrogenation and Hydrogenolysis. Acc. Chem. Res. (2021). 54 (9), 2144-2157. https://doi.org/10.1021/acs.accounts.1c00013
(A. Bordet, D. Kalsi, W. Leitner)
- Deutsche Forschungsgemeinschaft (German Research Foundation) under Germany ́s Excellence Strategy – Exzellenzcluster 2186 ‘The Fuel Science Center’ (ID: 390919832)
- Max-Planck-Gesellschaft (Max Planck Society)