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Mixed nanocrystalline Ce-Zr-O oxides (Ce/Zr = 1 or 7/3) were prepared by modified Pechini route using ethylene glycol solutions of metal salts. Detailed characterization of their real structure and surface properties by X-ray diffraction on synchrotron radiation with the full-profile Rietveld analysis, high resolution electron microscopy with elemental analysis, Raman spectroscopy, UV-Vis and X-ray photoelectron spectroscopy revealed a high homogeneity of cations distribution in nanodomains resulting in stabilization of disordered cubic phase. This provides a high dispersion of NiO loaded on these mixed oxides by wet impregnation, a high reactivity and mobility of oxygen in these catalysts and strong interaction of Ni with support in the reduced state. This helps to achieve a high activity and coking stability of developed catalysts in CH4 dry reforming in feeds with CH4 concentration up to 15% and CH4/CO2 ratio =1.

A series of 5%Ni/Ce1-xTixO2 catalysts was prepared with nickel impregnation of mixed Ce–Ti oxides obtained via synthesis in supercritical isopropanol. All oxides have a cubic fluorite phase structure. Ti is incorporated into the fluorite structure. Small amounts of impurities of TiO2 or mixed Ce–Ti oxides appear with Ti introduction. Supported Ni is presented as the NiO or NiTiO3 perovskite phase. Ti introduction increases total samples reducibility and results in stronger interaction of supported Ni with the oxide support. The fraction of rapidly replaced oxygen and the average tracer diffusion coefficient also increase. The number of metallic nickel sites decreased with increasing Ti content. All catalysts except Ni-CeTi0.45 demonstrate close activity in tests of dry reforming of methane. The lower activity of Ni-CeTi0.45 can be connected to Ni decoration with species of the oxide support. The incorporation of Ti prevents detachment of Ni particles from the surface and their sintering during dry reforming of methane. [ABSTRACT FROM AUTHOR]

Two series of Ni/Ce(Ti/Nb)ZrO2 catalysts were prepared using citrate route and original solvothermal continuous flow synthesis in supercritical isopropanol and studied in dry reforming of methane (DRM). TEM, XPS and FTIRS of adsorbed CO confirm influence of support composition and preparation method on the catalysts' morphology and surface features. The oxygen mobility was studied by isotope heteroexchange with C18O2. After testing in DRM, carbon deposits after catalysts' testing in DRM were investigated by temperature-programmed oxidation with thermo-gravimetric analysis. The lowest amounts of carbon deposits were obtained for unmodified Ni-CeZr and Ni-CeNbZr compositions. Ti addition lead to an increased amount of carbon, which was removed at higher temperatures. The use of supercritical supports also resulted in the formation of a higher amount of coke. Catalysts prepared by the supercritical synthesis were tested in DRM for 25 h. The highest activity drop was observed in the first three hours. For all compositions, close values of carbon deposits were revealed. [ABSTRACT FROM AUTHOR]

The ordered mesoporous Mg- and Ni-Mg-alumina samples of general formula xwt%Mg-Al2O3 and ywt%Nixwt% Mg-Al2O3 (x, y = 5, 10 % wt) have been prepared by the one-pot evaporation induced self-assembly (EISA) method using Pluronic P123 as a template. The textural and structural properties of the prepared samples have been characterized by N2 adsorption-desorption analysis, BET, XRD, TEM with EDX, HAADF-STEM, and H2-TPR. The samples calcined at 700°C had an ordered mesoporous structure with a SSA of 170-250 m²/g, a pore volume of 0.5-0.64 cm³/g and a narrow distribution of the pore size (mean 12-16 nm). For the catalysts prepared by the one-pot EISA method, the size of the metal Ni particles was in the range of 3-12 nm and was conditioned by their confinement in the mesopores and the interaction with MgO and Al2O3. Testing in methane dry reforming in the 15v.% CH4+ 15v.%CO2 feed, with He balance, at 650-750°C and the contact time of 0.015 s has shown the higher activity and stability of the ordered mesoporous 10w%Ni-10w%Mg-v catalysts prepared by the one-pot method as compared with the catalyst of the same composition obtained by impregnation. [ABSTRACT FROM AUTHOR]

For Ni/CeZrO catalyst prepared in supercritical isopropanol main features of methane dry reforming reaction mechanism were studied by the pulse microcalorimetric technique. The reaction scheme is described by a step-wise redox mechanism with independent stages of CH4 transformation on Ni/support interface producing syngas with participation of support oxygen bridging species (the rate-limiting stage) and fast reoxidation of support sites by CO2 yielding CO regenerating reactive oxygen species. [ABSTRACT FROM AUTHOR]

The Ni-containing catalysts based on ceria–zirconia doped with Ti and Ti+Nb were prepared by the solvothermal method in supercritical fluids. Ni deposition was carried out by incipient wetness impregnation and the one-pot technique. All materials were investigated by a complex of physicochemical methods (XRD, BET, TEM, H2-TPR). Samples catalytic properties were studied in methane dry reforming in the plug-flow reactor. Conversions of CH4 and CO2, H2/CO ratio, and CO and H2 yields were measured, and detailed kinetics analysis was carried out. The influence of Ni loading method and support modification on the catalytic behavior in the methane dry reforming process was studied. The preparation method of catalysts affects the textural characteristics. For one-pot samples, pore volume and surface area are lower than for impregnated samples. For catalysts on modified supports, strong metal–support interaction was shown to increase catalytic activity. A reduction pretreatment of samples was shown to have significant influence on their catalytic properties. The kinetic parameters such as reaction rate constant at 700 °C, effective activation energy, and TOF were estimated and analyzed. [ABSTRACT FROM AUTHOR]

A series of 5%Ni-CexZr1−xO2 (x = 0.3, 0.5, 0.7) catalysts has been prepared via one-pot solvothermal continuous synthesis in supercritical isopropanol and incipient wetness impregnation of CexZr1−xO2 obtained by the same route. The textural, structural, red-ox, and catalytic properties in methane dry reforming (MDR) of Ni-modified Ce-Zr oxides synthesized by two routes have been compared. It was shown by XRD, TEM, and Raman spectroscopy that the method of Ni introduction does not affect the phase composition of the catalysts, but determines the dispersion of NiO. Despite a high dispersion of NiO and near-uniform distribution of Ni within Ce-Zr particles observed for the one-pot catalysts, they have shown a lower activity and stability in MDR as compared with impregnated ones. This is a result of a low Ni concentration in the surface layer due to segregation of Ce and decoration of nickel nanoparticles with support species. [ABSTRACT FROM AUTHOR]

Nickel-containing mixed ceria-zirconia oxides also doped by Nb and Ti have been prepared by a citrate route and by original solvothermal continuous flow synthesis in supercritical alcohols. Nickel was subsequently deposited by conventional insipient wetness impregnation. The oxides are comprised of ceria-zirconia solid solution with cubic fluorite phase. Negligible amounts of impurities of zirconia are observed for samples prepared by citrate route and doped by Ti. Supports prepared by supercritical synthesis are single-phased. XRD data, Raman, and UV-Vis DR (diffuse reflectance) spectroscopy suggest increasing lattice parameter and amount of oxygen vacancies in fluorite structure after Nb and Ti incorporation despite of the preparation method. These structural changes correlate with the catalytic activity in a methane dry reforming reaction. Catalysts synthesized under supercritical conditions are more active than the catalysts of the same composition prepared by the citrate route. The catalytic activity of samples doped with Ti and Nb is two times higher in terms of TOF (turnover frequency) and increased stability of these catalysts is attributed with the highest oxygen mobility being crucial for gasification of coke precursors. [ABSTRACT FROM AUTHOR]