Synthesis of Ni/NiAlOx Catalysts for Hydrogenation Saturation of Phenanthrene

The saturation of octahydrophenanthrene was the rate-determining step in the hydrogenation process from phenanthrene to perhydrophenanthrene, which was due to the steric hindrance and competitive adsorption of octahydrophenanthrene. In this work, a series of Ni/NiAlOx catalysts with a uniform electron-deficient state of Ni derived from the nickel aluminate structure was synthesized to overcome the disadvantage of noble catalyst and the traditional sulfided catalysts in the saturation hydrogenation process of phenanthrene. Results showed that the catalyst calcinated at 650°C possessed more Ni2+ (∼98%) occupying octahedral sites and exhibited the highest robs (1.53 × 10−3 mol kg−1 s−1) and TOF (14.64 × 10−3 s−1) for phenanthrene hydrogenation. Furthermore, its ability to overcome steric hindrance and promote the rate-determining step was proven by octahydrophenanthrene hydrogenation. Comparing the evolution of hydrogenation activity with the change in the electronic structure of surface Ni sites, it was shown that the increase of metallic electron deficiency hindered the π-back bonding between surface Ni and aromatic rings, which was unfavorable for aromatic adsorption. As a result, the phenanthrene hydrogenation saturation performance can be enhanced by stabilizing the electron-deficient state of surface Ni on an optimal degree.

Tuning Metal–Support Interactions on Ni/Al2O3 Catalysts to Improve Catalytic Activity and Stability for Dry Reforming of Methane

Ni-based catalysts supported on alumina derived from the pseudo-boehmite prepared by the impregnation method were employed for catalytic dry reforming of methane reaction at the temperature of 550–750 °C. The effect of calcination temperature on physicochemical properties such as the Ni dispersion, reduction degree, nickel crystallite sizes, and metal–support interaction of the catalysts was investigated. The characterization results show that increasing the catalyst calcination temperature leads to the formation of nickel-alumina spinel, which enhances the metal–support interaction and increases the reduction temperature. The nickel nanoparticle size decreases and the effective dispersion increases with the increasing calcination temperature from 450 °C to 750 °C due to the formation of nickel aluminate. The catalyst calcined at 750 °C exhibits the highest CH4 and CO2 conversion owing to the small Ni0 active sites and high Ni dispersion. In a 200 h stability test in dry reforming of methane at 700 °C, the Ni/Al2O3-750 catalyst exhibits excellent catalytic stability and anti-coking ability.

Rare-Earth Metals-Doped Nickel Aluminate Spinels for Photocatalytic Degradation of Organic Pollutants

Visible-light-activated photocatalysts based on samarium-doped, europium-doped, and gadolinium-doped nickel aluminates (SmNA, EuNA, GdNA) were synthesized. The spinel crystalline structures of the doped mixed metal oxides were demonstrated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. The presence of the rare-earth metals (REMs) was confirmed by the energy-dispersive X-ray (EDX) studies. Ultraviolet-visible-near-infrared (UV-Vis-NIR) spectra revealed that the REMs-doped catalysts absorb in the full solar spectrum range covering both visible and near infrared wavelengths. Scanning electron microscopy (SEM) visualized the profound morphological alterations of the doped nickel aluminate samples. Consequently, the pore volume and the Brunauer-Emmett-Teller (BET) surface area decreased, while nanoparticles sizes increased. Fourier-transform infrared spectroscopy (FTIR) exposed that surfaces of REMs-doped nickel aluminates are rich in hydroxyl groups. Finally, the photocatalytic performance was notably increased through doping nickel aluminate (NA) with REMs; the highest activity was observed for EuNA.

Nanostructured Nickel Aluminate as a Key Intermediate for the Production of Highly Dispersed and Stable Nickel Nanoparticles Supported within Mesoporous Alumina for Dry Reforming of Methane

Two routes of preparation of mesoporous Ni-alumina materials favoring the intermediate formation of nanostructured nickel-aluminate are presented. The first one involves an aluminum containing MOF precursor used as sacrificial template to deposit nickel while the second is based on a one-pot synthesis combined to an EISA method. As shown by a set of complementary techniques, the nickel-aluminate nanospecies formed after calcination are homogeneously distributed within the developed mesoporous alumina matrices whose porous characteristics vary depending on the preparation method. A special attention is paid to electron-microscopy observations using especially STEM imaging with high chemical sensitivity and EDS elemental mapping modes that help visualizing the extremely high nickel dispersion and highlight the strong metal anchoring to the support that persists after reduction. This leads to active nickel nanoparticles particularly stable in the reaction of dry reforming of methane.