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The nature of the Ni(II) phase formed on silica during the preparation by deposition−precipitation (DP) of Ni/SiO2 samples is shown to depend on the silica surface area and the time of deposition−precipitation. Ni/SiO2 samples have been characterized by XRD, IR, EXAFS, TPR, TEM, STEM-EDX, and BET. With silica of low surface area and for short DP time (≤4 h), the Ni(II) phase is mainly a turbostratic nickel hydroxide with a small amount of 1:1 nickel phyllosilicate. With silica of high surface area and for short DP time (≤100 min), the Ni(II) phase is mainly a 1:1 nickel phyllosilicate. For longer DP time (>4 h) and with both types of silica, the Ni(II) phase is an ill-crystallized 1:1 nickel phyllosilicate. However, the latter is better crystallized with silica of low surface area. Almost the same Ni(II) phases were obtained whether silica was porous or not. However, the Ni(II) phase is better crystallized and the interface with the support is larger with nonporous silica than with porous one.

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Low-coordinated (LC) ions at the MgO surface (noted Mg2+LC and O2-LC with L = 1-5), located on monatomic and diatomic steps, corners, step divacancies, and kinks, have been modeled thanks to periodic density functional theory (DFT) calculations (VASP). Ions of lowest coordination induce the strongest surface geometry relaxation and the highest surface energies. The hydration energies of these sites and thermodynamic stabilities of the resulting surfaces were studied. The factors controlling the interaction strength between water and the surface are the possibility for the hydroxyl group to adopt a bridging geometry between two Mg2+ cations in concave areas of the surface, such as the bottom of the monatomic step, and at second order the surface atomic coordination, and especially the presence of three-coordinated ions. The Lewis basicity and acidity of O2-LC and Mg2+LC, respectively, increase as their coordination number decreases, which implies the same trend for the Brønsted basicity of the Mg2+-O2- pair toward water. However, this trend can be changed if pairs leading to the formation of bridging OH groups are involved, typically on monatomic steps or in step divacancies where O2C-H and O3C-H are obtained, respectively, instead of the expected O1C-H. Thanks to thermodynamic calculations, the state of the surface as a function of temperature can be determined at a given pressure, unraveling the roles of surface topology and ions coordination.

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The infrared OH stretching frequencies of the various types of hydroxyl groups on MgO surfaces have been calculated by periodic (VASP) and cluster (Gaussian) DFT simulations. Surface irregularities (mono and diatomic steps, corners, step divacancies, and kinks) have been considered to model the IR spectra of hydroxylated MgO powders. A good correspondence between calculated and experimental frequencies is obtained with the B3LYP functional. Hydrogen-bonding is the parameter which influences most the IR frequency of OH groups, followed by location of OH groups in concave or convex areas of the surface and then oxygen coordination. The evolution of experimental IR spectra upon evacuation at increasing temperature can be rationalized on the basis of calculated thermal stabilities of each kind of OH groups. A new model is finally proposed to help assign the experimental bands, in terms of hydrogen-bonding, local topology of the hydroxylated sites, and coordination of oxygen.

The characterization of the coordination geometry of copper ions included within zeolites has been carried out with a combination of in-situ XAFS, photoluminescence, and IR measurements in order to obtain a detailed description of the formation of isolated Cu+ monomers with planar 3-coordinate or linear 2-coordinate geometry in the zeolite channels by thermal treatment under vacuum. The Cu+ ions within the zeolites were found to exist as isolated Cu+ monomers and (Cu+−Cu+) dimers, their relative concentrations strongly depending on the type of zeolite used. With ZSM-5 and mordenite zeolites, most of the copper cations were found to exist as isolated Cu+ monomers, in contrast to the case of the Y-zeolite. CO molecules were adsorbed selectively only on isolated Cu+ monomers, distorting the coordination geometry to form stable one-on-one Cu+−CO complexes.

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