Papers by Keyword: Mixed Oxides

Abstract: Improvements of the catalytic efficiency of nickel–aluminum oxides in reforming reactions for hydrogen production have been achieved by the development of synthesis processes that provide powders with high surface area. The reduction of the crystallization temperature is one of the procedures in this direction. In this work, the effect of solvothermal treatment on coprecipitated gels with 15 wt% nickel content in alumina matrix was evaluated. Powders were obtained by coprecipitation with and without treatment of gels under n-butanol vapor pressure at 150oC. Products were characterized by TG/DTA, X-ray diffraction, specific surface area measurements, scanning electron microscopy and laser beam scattering for granulometric distribution determination. The results showed that calcined powders have high specific surface area (ranging from 170 to 260 m².g^-1) and are composed by gamma alumina and nickel aluminate phases. Aging treatment did not promote hydroxides decomposition under solvothermal conditions, indicating the need of calcination step.

Abstract: Micro-mesoporous mixed oxides containing nickel, cobalt and aluminum have been synthesized using conventional coprecipitation method. FESEM and HRTEM analyses demonstrated the flower and hexagonal plate-like nanostructured of mixed oxides. Different mixed oxide formation, homogenous metal dispersion, textural properties were investigated using XRD, ICP-MS and BET (N₂ adsorption-desorption) techniques. nanostructured mixed oxides exhibited 2.6 wt% hydrogen adsorption that were studied using temperature programmed reduction-adsorption-desorption (H₂-TPR/TPD) and thermogravimetric and differential thermal analysis (TGA-DTA) techniques. Investigation corresponds that morphologies, textural properties and surface energy of mixed oxides are important in hydrogen adsorption.

Abstract: nanostructured hydrotalcite-like compounds that contain nickel, cobalt and aluminum have been synthesized by conventional coprecipitation method without using any surfactants or templating agents. The structure and morphology of the coprecipitated nanohydrotalcites and its derived mixed oxides were characterized by powder X-ray diffraction (XRD), Fourier-transformed Infrared (FTIR) spectroscopy, field-emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and nitrogen adsorption-desorption techniques. The results show that the synthesized materials exhibited micro-meso-pore networks. The cobalt-rich calcined hydrotalcites are generally amorphous, having a coral-like morphology whereas nickel-rich hydrotalcites show hexagonal plate-like morphology. The presence of nickel in mixed oxides catalyzed the reduction of Co-Al-O spinels. The Fast Fourier Transform (FFT) analysis of HRTEM revealed the inter planner distances of the crystal of hydrotalcite.

Abstract: CuMgAl hydrotalcite-like compounds with MII/MIII=1 and Cu/Mg molar ratios 3:1, 1:1, 1:3 and 1:19 were synthesized by coprecipitation and characterized by elemental analyses, XRD, SEM, FT-IR, TG-DTA and BET surface area test. XRD of all samples showed that Cu/Mg/Al hydrotalcites without any detectable impurity phase could be obtained at Cu/Mg molar ratios 1:3 and 1:19, however, at high Cu/Mg molar ratios 3:1 and 1:1, Al(OH)3 and copper hydroxides or oxides were obtained in the products besides the hydrotalcites, owing to the strong Jahn-Teller effect of Cu2+. It was also found that the crystallinity of the solids increased with an increase in copper content. IR results showed that the symmetry of carbonate was reduced from D3h to lower symmetry at high copper content. The thermal stability of the compounds decreased with increasing copper content, as indicated by TG-DTA measurements. Further thermal decomposition analyses showed that the surface area reached the maximum at calcination temperature of 500 ° C and mixed metal oxides with crystalline MgO, amorphous Al2O3 and highly dispersed CuO were obtained.

Abstract: In this overview, we discuss the sum-rule relating phenomenological coefficients in randomly mixed systems and consider several applications to collective diffusion problems. These applications include intrinsic diffusion multicomponent alloys, chemical diffusion in strongly ionic mixed cation crystals and demixing of cations in randomly mixed quaternary transition metal oxides. In each case a substantial simplification is possible as a result of the sum-rule.