Nickel ferrite spinel as catalyst precursor in the dry reforming of methane:Synthesis,characterization and catalytic properties

Dry reforming of methane by CO2 using nickel ferrite as precursor of catalysts was investigated.Nickel ferrite crystalline particles were prepared by coprecipitation of nitrates with NaOH or ammonia followed by calcination,or by hydrothermal synthesis without calcination step.The textural and structural properties were determined by a number of analysis methods,including X-ray diffraction （XRD）,Raman spectroscopy and X-ray photoelectron spectroscopy （XPS）,among which X-ray diffraction （XRD） was at room and variable temperatures.All synthesized oxides showed the presence of micro or nanoparticles of NiFe2O4 inverse spinel,but Fe2O3 （hematite） was also present when ammonia was used for coprecipitation.The reducibility by hydrogen was studied by temperature-programmed reduction （TPR） and in situ XRD,which showed the influence of the preparation method.The surface area （BET）,particle size （Rietveld refinement）,as well as surface Ni/Fe atomic ratio （XPS） and the behavior upon reduction varied according to the synthesis method.The catalytic reactivity was investigated using isopropanol decomposition to determine the acid/base properties.The catalytic performance of methane reforming with CO2 was measured with and without the pre-treatment of catalysts under H2 in 650-800 C range.The catalytic conversions of methane and CO2 were quite low but they increased when the catalysts were pre-reduced.A significant contribution of reverse water gas shift reaction accounted for the low values of H2 /CO ratio.No coking was observed as shown by the reoxidation step performed after the catalytic reactions.The possible formation of nickel-iron alloy observed during the study of reducibility by hydrogen was invoked to account for the catalytic behavior.

Solvent-free synthesis of alumina supported cobalt catalysts for Fischer–Tropsch synthesis

A novel mechano-synthesis method has been elaborated in this work for the design of efficient cobalt-based Fischer–Tropsch catalysts. The process aims to reduce the total number of steps involved in the synthesis of solid catalysts and thus to avoid relevant toxic solutions generated during the catalyst preparation. The mechano-synthesis of the Co/Al2O3catalyst was processed in a low-energy vibratory micro mill and high energy planetary ball mill. Porous spherical γ-aluminas (1860 µm and 71 µm mean particle diameter) were used in this work as host compounds. Co3O4(3 µm mean particle diameter) has provided guest particles for mechano-synthesis. The catalysts were characterized by textural (surface area, porosity and particle size) and structural analyses (X-ray diffraction, TPR, SEM-EDX and microprobe). The microprobe images show deposition of Co3O4on the surface of the alumina and indicated no Co3O4diffusion inside the alumina pores. SEM-EDX mapping illustrated that cobalt coating tended to occur on surface of rounded shape of cracked alumina fragments. After milling, the crystallite size of Co3O4decreased to 15 nm from 30 to 50 nm. The TPR profiles indicated very low concentrations of inactive cobalt aluminate mixed compounds which are usually produced during the catalyst preparation by impregnation. In Fischer–Tropsch synthesis, the catalysts prepared using mechano-synthesis methods showed catalytic performance comparable to the catalysts prepared by impregnation. © 2016 Science Press

Keggin-type H_4PVMo_(11)O_(40)-based catalysts for the isobutane selective oxidation

Cesium heteropolysalts Cs3PMo12O40 and HCs3PVMo11O40 were synthesized by modifying the preparation conditions in order to get materials with a much higher surface area than the original Keggin-type heteropolyacids(H3PMo12O40 and H4PVMo11O40).These solids were used as carriers for the dispersion of H4PVMo11O40 heteropolyacid by the incipient wetness impregnation technique.The textural and structural properties of supports and catalysts were examined by scanning electron microscopy,N2 adsorption-desorption isotherms and Raman spectroscopy.The supported catalysts were studied before and after red/ox pretreatments by X-ray photoelectron spectroscopy,which showed that both the surface composition and oxidized to reduced species ratio depend on the used carrier.The catalytic performances of these novel supported catalysts in the selective oxidation of isobutane to methacrylic acid and methacrolein were studied.The best catalytic properties were obtained when H4PVMo11O40 was supported on HCs3PVMo11O40.The isobutane conversion and yield of the desired oxygenates increased along the unsupported H4PVMo11O40【H4PVMo11O40/Cs3PMo12O40【H4PVMo11O40/HCs3PVMo11O40 series.

Synthesis and characterization of La Ni_xCo_(1–x)O_3: Role of microstructure on magnetic properties

Perovskite-type structures with the composition La Ni x Co1–x O3（x=0.3, 0.5, 0.7） were synthesized by a modified sol-gel method. Using transitional metal elements on the lanthanum base perovskites, properties could be tuned by doping the structure. Thermogravimetric analysis（TGA） evidenced a temperature of 350 °C as the start point of the perovskite-phase formation. Scanning electron microscopy（SEM） images showed the microstructure changes（grain size） of the cobalt-doped perovskite due to composition. In addition, it was shown that magnetic properties of the samples were dependent of cobalt content; experimental results pointed to the existence of disordered spins interactions, which were more evident with the decrease of cobalt content and the existence of ferromagnetic coupling among spins of the samples. These results showed the feasibility of producing a family of compounds with the desired properties, manipulating composition and therefore the microstructure.