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Catalysis, reactivity, surfaces

The team leads a strong and well-recognized activity on the theoretical description of chemical reactivity in close relation with societal and economical questions on sustainable development, energy and environment. 

A strong effort is focussed on the understanding of elementary steps on solid catalysts. The catalytic transformation of biomass was a topic of strong focus in the period for C. Michel and P. Sautet, in interaction with experimental groups (IRCELYON, Lodz university). This mainly concerns mechanism and pathways of transformation of alcohols, polyols (glycerol) and other oxygenates (levulinic acid) extracted from the cellulosic part of biomass on the surface of transition metal catalysts. Our study has revealed the direct assistance of the water, just a solvent in principle, and for polyacohols of intramolecular hydrogen bonds, on the catalytic reaction of the oxygenate molecule. More recently in the framework of the LIA FUNCAT with Ottawa, the study of transformation of aromatic molecules extracted from lignin has been initiated in collaboration between surface science and DFT. In the context of Green Chemistry, the CO2 valorisation is also a very challenging task. We have explored pathways for the activation of CO2 to form CC bond with unsaturated molecules such as the production of acrylic acid from CO2 and ethylene. In collaboration with Solvay, two potential approaches: homogeneous catalysis and electrochemical coupling. 

The exploration of reaction pathways for hydrogenation/dehydrogenation reactions on transition metal surfaces remained a topic of strong interest for D. Loffreda, F. Delbecq and P. Sautet, finding new pathways for hydrogenation and isomerisation of unsaturated compounds. Reaction dynamics was studied for the “simple” case of methane on transition metal surfaces, enabling to understang how the reaction selectivity depends on vibrational excitations as shown by W. Dong.

Modelling catalysts and catalytic reactions in structures or conditions close to that of experiments is also an original focus of the group. This includes the description of catalysts at finite temperature under a pressure of gas, determining for example in combination with XAS and XPS experiments at the synchrotron the phases and the surfaces of iron carbide present in Fischer-Tropsch synthesis. Another combination with experiments allowed us to understand the nature of the sites active for methane activation on alumina and the importance of partial hydroxylation (P. Sautet, F. Delbecq). Beyond the gas-solid interface, the liquid-solid one is also a key for many applications in catalysis and this complex interface was attacked with AIMD (D. Loffreda) or with adaptive QM/MM methods (P. Fleurat-Lessard, R. Bulo as a former member of the group). Realism also concerns the description of the morphology catalyst, with the study of the structure and reactivity of nanometer size transition metal particles deposited on oxide supports (alumina, ceria). We showed, in collaboration with IFPEN, that the shape of the particle is influenced by the support and the presence of adsorbates, while in return catalytic properties of the nanosize particles are modified compared to the case of extended surfaces.

In the field of energy applications, fuels cells and batteries also require catalytic devices. For catalyst design, fast and accurate predictions of chemical reactivity on nanoparticles are paramount. Current theoretical models use electronic-structure-based descriptors with known limitations. We demonstrated that the adsorption energetics of oxygenated species on various platinum nanoparticles and extended surfaces are linearly captured by a simple and powerful descriptor: the generalized coordination number. (D. Loffreda, P. Sautet).

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