Catalysis and Surface Organometallic Chemistry: A View from Theory and Simulations

Recent NMR developments applied to organic-inorganic materials

In this contribution, the latest developments in solid state NMR are presented in the field of organic-inorganic (O/I) materials (or hybrid materials). Such materials involve mineral and organic (including polymeric and biological) components, and can exhibit complex O/I interfaces. Hybrids are currently a major topic of research in nanoscience, and solid state NMR is obviously a pertinent spectroscopic tool of investigation. Its versatility allows the detailed description of the structure and texture of such complex materials. The article is divided in two main parts: in the first one, recent NMR methodological/instrumental developments are presented in connection with hybrid materials. In the second part, an exhaustive overview of the major classes of O/I materials and their NMR characterization is presented.

Ligand-field theory-based analysis of the adsorption properties of ruthenium nanoparticles

The experimental design of improved nanocatalysts is usually based on shape control and is surface-ligand dependent. First-principle calculations can guide their design, both in terms of activity and selectivity, provided that theoretical descriptors can be defined and used in a prescreening process. As a consequence of the Sabatier principle and of the Brønsted-Evans-Polanyi relationship, an important prerequisite before optimizing the catalytic properties of nanoparticles is the knowledge of the selective adsorption strengths of reactants at their surface. We report here adsorption energies of X (H, CH3) and L (PH3, CO) ligands at the surface of bare ruthenium nanoclusters Run (n = 55 and 147) calculated at the DFT level. Their dependence on the topology of the adsorption sites as well as on the size and shape of the nanoparticles (NPs) is rationalized with local descriptors derived from the so-called d-band center model. Defining the descriptors involves the determination of the energy of effective d atomic orbitals for each surface atom. Such a ligand field theory-like model is in close relation with frontier molecular orbital theory, a cornerstone of rational chemical synthesis. The descriptors are depicted as color maps which straightforwardly yield possible reactivity spots. The adsorption map of a large spherical hcp cluster (Ru288) nicely confirms the remarkable activity of steps, the so-called B5 sites. The predictive character of this conceptual DFT approach should apply to other transition metal NPs and it could be a useful guide to the design of efficient nanocatalysts bearing sites with a specific activity.

Chemistry with methane: concepts rather than recipes

Four seemingly simple transformations related to the chemistry of methane will be addressed from mechanistic and conceptual points of view: 1) metal-mediated dehydrogenation to form metal carbene complexes, 2) the hydrogen-atom abstraction step in the oxidative dimerization of methane, 3) the mechanisms of the CH(4)→CH(3)OH conversion, and 4) the initial bond scission (C-H vs. O-H) as well as the rate-limiting step in the selective CH(3)OH→CH(2)O oxidation. State-of-the-art gas-phase experiments, in conjunction with electronic-structure calculations, permit identification of the elementary reactions at a molecular level and thus allow us to unravel detailed mechanistic aspects. Where appropriate, these results are compared with findings from related studies in solution or on surfaces.