Theoretical approaches of chemical reactivity at surfaces: selective reactions (chemoregioselective, enantioselective reactions on metallic catalysts and oxide support) but also simple hydrogenation and oxidation catalytic processes.
Density-functional theory (periodic systems such as crystals and surfaces)
Condensed matter theory (energetics and phonons)
Simulations of vibrational spectra of adsorbates (EELS, IRAS)
Transition-state theory and microkinetic models
General research fields:
Chemistry & physics of surfaces and interfaces
Heterogeneous catalysis and quantum mechanics
Some recent "highlights" from my research activities
Selective and partial oxidation of ethene on silver oxide surface (M.-L. Bocquet, D. Loffreda, JACS, (2005)). From density-functional theory calculations (VASP code, G. Kresse, J. Hafner), the oxidation pathways of the ethene educt on a AgxO surface oxide have been investigated. The CI-NEB (Climbing-Image Nudged Elastic Band) methodology coupled with a microkinetic model has allowed to solve the question of the selectivity between the epoxide and the acetaldehyde competitive products. Hereafter, a Quicktime movie illustrating the first oxidation step (formation of the oxametallacycle key intermediate) is shown.
Competitive hydrogenations routes of acrolein (propenal) on the Pt(111) surface (D. Loffreda, F. Delbecq, F. Vigné, P. Sautet, JACS, (2006), & Angewandte Chemie, International Edition, (2005)). The complex mechanism has been explored completely with density-functional theory with VASP and the CI-NEB method evoked before. In contrast with the accepted empirical rule, the hydrogen attacks at the C=O bond are always less energetic than those at the C=C bond. For the hydrogenation at the C=O moiety, the mechanism is non classical and intermediate between Langmuir-Hinshelwood and Rideal-Eley. In the following Quicktime movie, such a route is presented for the first hydrogen attack at the C=O bond, yielding the hydroxyallyl surface species (the energy unit is eV and the distance unit is Å).
Preferential oxidation of CO molecule on fuel cell catalysts. The efficiency of the PtSn surface catalysts towards CO oxidation has been evidenced by DFT calculations (C. Dupont, Y. Jugnet, D. Loffreda, JACS (2006)). The microkinetic analysis has shown that the PtSn deposit on Pt(111) outstrips in activity the Pt(111) surface by several orders of magnitude at 300 K, in agreement with experimental observations. The specific role of Sn has been mentioned and explained on the basis of a generalisation of the Hammer's energetic decomposition model.
Molecular recognition of multifunctional compounds on metallic surfaces. The identification of the adsorbate structures on model catalytic surfaces is an every-day hard task, both at the experimental and theoretical levels (D. Loffreda, Y. Jugnet, F. Delbecq, J.-C. Bertolini, P. Sautet, JPCB (2004) & D. Loffreda, Angewandte Chemie International Edition (2006)). For multifunctional conjugated molecules, the interpretation of routine IRAS or RAIRS spectra is even more complicated since the adsorption forms are often almost flat on the surface and several structures usually compete at the energetic level. Different strategies have been developed in the recent years to tackle such a problem. Among them, the comparison between experimental IR spectra and DFT calculations seems mandatory to advance in the molecular recognition at surfaces. Here below, a Quicktime movie exposes an example of a DFT computed vibration (C=O stretching mode) for a peculiar adsorption structure of prenal on Pt(111).
Enantioselective hydrogenation of alpha-ketoesters on chirally modified metallic surfaces. The chemisorption of cinchonidine auxiliary modifier is shown on a platinum substrate in periodic conditions.
