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The hydrogenation of HCN to methylamine on Co(111) was used as a model reaction to study the hydrogenation of nitriles to primary amines. Density functional theory was used to characterize the reaction mechanism, and the results obtained were compared with those for the same reaction on Ni(111). Hydrogen cyanide adsorbs more strongly on Co(111) than on Ni(111), with an adsorption energy of -1.72 eV. The hydrogenation product, methylamine, is weakly adsorbed on Co(111), with an adsorption energy of -0.53 eV, which is very similar to the adsorption energy calculated on Ni(111). The calculated adsorption energies were used to explain the differences in activity and selectivity observed between nickel- and cobalt-based catalysts; the stronger adsorption of HCN on cobalt explains both the lower activity and the higher selectivity observed on this metal. Regarding the reaction mechanism, the hydrogenation reaction implies an imine intermediate (H2CNH) independent of whether hydrogen reacts with the carbon atom or with the nitrogen atom of the hydrogen cyanide molecule in the first step. The imine intermediate subsequently reacts to form H3CNH, which is finally hydrogenated to yield methylamine. The overall surface reaction is endothermic. Remarkably, comparing the HCN hydrogenation reaction mechanism on Co(111) and Ni(111) revealed no significant differences.

National @ BIOVERT+PFO; International audience; None

International @ BIOVERT+PFO; International audience; None

International @ BIOVERT+PFO; International audience; None

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The adsorption and dissociation of CO has been calculated on the surface plane of the body centered cubic (BCC) transition-metals Fe, Mo, Cr, and W using density functional theory (DFT) for two CO coverages; 0.25 and 0.5 ML. The coverage effect will be discussed for the adsorption energy, tilting angle, and stretch frequency of CO. Furthermore, the effect of coverage will be presented by means of complete energy diagrams of the dissociation reaction of tilted CO on all four metals. Lastly, we will show that scaling relations apply to a bent CO species on all four transition metals as well as the metal-alloys Fe3Mo and Fe3Cr, in the sense that heat of adsorption of CO and the activation energy of CO dissociation scale linearly with the heat of adsorption of the carbon.

The 4f¿5d absorption and emission spectra of Ce3+-doped YAG (Y3Al5O12) are simulated with a quantum chemical ab initio embedded cluster approach applied to Ce3+ substitutional defects of D2 local symmetry. The only empirical information used is the structure of the pure host. The simulated absorption spectrum is calculated with overestimations of 2300–, which became in the luminescence. The three 4f¿5d observed absorptions were assigned and the energies of the two remaining ones, which are hidden by the absorption of the pure host, were predicted. The lowest 5d¿4f emission was found to take place from G5 (22A) and the next emission from G5 (32B3). Good absorption and emission band shapes and relative intensities are obtained. A large underestimation of the Stokes shift is found, which suggests an underestimation of the relaxation on the emitting state.

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New Zn-based catalysts are described that act as heterogenized or heterogeneous catalysts, with easy recovery and re-utilization with a limited or even zero Zn-leaching. For stabilizing in the heterogeneous form the catalytically active Zn centre, mixed oxides, ZIF-8 and Zn-tethered systems have been synthesized and found to sensibly reduce the leaching of Zn in solution with respect to ZnO, making possible their recovery and reuse. ZIF-8 can be used for long time of reaction, reaching high DEC yields (comparable or higher than those obtained with ZnO) without any significant loss of zinc.