A systematic study of the interactions between chemical partners (metal, ligands, counterions, and support) involved in the design of Al2O3-supported nickel catalysts from diamine-Ni(II) chelates

1.5 Ni wt %/Al2O3 catalysts have been prepared by incipient wetness impregnation using [Ni(diamine)x(H2O)(6-2x)]Y2 precursors (diamine = 1,2-ethanediamine (en) and trans-1,2-cyclohexanediamine (tc); x = 0, 1, and 2; Y = NO3- and Cl-), to avoid the formation, during calcination, of difficult-to-reduce nickel aluminate. N2 was chosen for thermal treatment to help reveal and take advantage of the reactions occurring between Ni2+, ligands, counterions, and support. In the case of [Ni(en)2(H2O)2]Y2 salts used as precursors, in situ UV-vis and DRIFT spectroscopies show that after treatment at 230 degrees C Ni(II) ions are grafted to alumina via two OAl bonds and that the diamine ligands still remain coordinated to grafted nickel ions but in a monodentate way, bridging the cation with the alumina surface. With Y = Cl-, the chloride counterions desorb as hydrogen chloride, and hydrogen released upon decomposition of the en ligands is able to reduce a fraction of nickel ions into metal as evidenced by XPS. In contrast, with Y = NO3-, compounds such as CO or NO are formed during thermal treatment, indicating that nitrate ions burn the en ligands. After thermal treatment at 500 degrees C, a surface phase containing Ni(II) ions forms, characterized by XPS and UV-vis spectroscopy. Temperature-programmed reduction shows that these ions can be quantitatively reduced to the metallic state at 500 degrees C, in contrast with the aluminate obtained when the preparation is carried out from [Ni(H2O)6]2+, which is reduced only partly at 950 degrees C. On the other hand, a total self-reduction of nickel complexes leading to 2-5-nm metal particles is obtained upon thermal treatment via the hydrogen released by a hydrogen-rich ligand such as tc, whatever the Y counterion. An appropriate choice of the ligand and the counterion allows then to obtain selectively Ni(II) ions or a dispersed reduced nickel phase after treatment in N2, as a result of the reactions occurring between the chemical partners present on alumina.     

A least square finite element formulation of the collimated irradiation in frequency domain for optical tomography applications

This paper presents an extension of the least square finite element formulation associated to the discrete ordinates method to solve collimated irradiation problems in frequency domain. The features of the method are shown with a separation of the intensity into its collimated and scattered parts for a better handling of discontinuities due to the boundary conditions of Dirichlet type used in optical tomography applications. Numerical tests are used to gauge the accuracy of the model in both isotropic and anisotropic scattering media, with and without frequency modulation. The results show that the method is accurate compared to some reference solutions.     

Filamentation “remote” sensing of chemical and biological agents/pollutants using only one femtosecond laser source

All matters in the path of filaments induced by an intense femtosecond laser pulse propagating in air could be fragmented and result in the emission of characteristic fluorescence spectra from the excited fragments. The fluorescence spectra exhibit specific signatures (fingerprints) that can be used for the identification of various substances including chemical and biological species. In this paper, we present an overview of the recent progress in our laboratory concerning the “remote” sensing of chemical and biological agents/pollutants in air using filamentation-induced nonlinear fluorescence techniques.     

A simple method to significantly increase filaments’ length and?ionization density

A simple method to produce longer filaments with higher ionization density in air by controlling the diameter of an aperture in the laser beam path is studied via an analysis of the backscattered N₂ fluorescence collected by LIDAR. Significant increase in the fluorescence signal (approximately by a factor of five depending on the conditions) and an increased filament length was observed at an optimum diameter. 3D + time stochastic numerical simulations have shown that the optimum aperture size corresponds to the case of multiple filament ‘squeezing’ around the propagation axis forming the regularized elongated structure with higher overall amount of plasma. The optimum range of aperture sizes is the same for the initial transverse perturbation scale variation at least within a factor of three.     

Machine learning and signed particles,an alternative and efficient way to simulate quantum systems

Recently neural networks have been applied in the context of the signed particle formulation of quantum mechanics to rapidly and reliably compute the Wigner kernel of any provided potential. Important advantages were introduced, such as the reduction of the amount of memory required for the simulation of a quantum system by avoiding the storage of the kernel in a multi-dimensional array, as well as attainment of consistent speedup by the ability to realize the computation only on the cells occupied by signed particles. An inherent limitation was the number of hidden neurons to be equal to the number of cells of the discretized real space. In this work, anew network architecture is presented, decreasing the number of neurons in its hidden layer, thereby reducing the complexity of the network and achieving an additional speedup. The approach is validated on a onedimensional quantum system consisting of a Gaussian wave packet interacting with a potential barrier.     

Evolution of nickel speciation during preparation of Ni-SiO(2) catalysts: effect of the number of chelating ligands in [Ni(en)x(H2O)6-2x]2+ precursor complexes

The evolution of nickel speciation during the successive preparation steps of Ni-SiO(2) catalysts is studied by UV-Vis-NIR, FT-IR, DTG, TPR and TEM. The study focuses on the effect of the number of chelating ligands in the precursor complexes [Ni(en)(x)(H(2)O)((6-2x))](2+) (en = ethylenediamine, x = 1, 2, 3) on the adsorption on silica, and on nickel speciation after thermal treatment. When the en:Ni ratio in solution increases from 1 to 3, the most abundant complex is [Ni(en)(H(2)O)(4)](2+) (64% of all Ni complexes), [Ni(en)(2)(H(2)O)(2)](2+) (81%) and [Ni(en)(3)](2+) (61%), respectively. Equilibrium adsorption of [Ni(en)(x)(H(2)O)((6-2x))](2+) on SiO(2) results in the selective grafting of [Ni(en)(H(2)O)(4)](2+) and [Ni(en)(2)(H(2)O)(2)](2+), through the substitution of two labile H(2)O ligands by two surface SiO(-) groups. The surface [Ni(en)(H(2)O)(2)(SiO)(2)] complex formed by the grafting of [Ni(en)(H(2)O)(4)](2+) onto silica tends to transform into NiO and nickel phyllosilicate after calcination, which consequently leads to large and heterogeneously distributed metallic Ni particles upon reduction. In contrast, [Ni(en)(2)(SiO)(2)], resulting from the grafting of [Ni(en)(2)(H(2)O)(2)](2+) onto silica, no longer has aqua ligands able to react with other nickel complexes or silicium-containing species. Calcination transforms these complexes into isolated Ni(2+) ions, which are reduced into small metallic Ni particles with a more homogeneous size distribution, even at higher Ni loading.