Mixed Oxide Matrix Research Articles

Optimization of nickel loading of mixed oxide catalyst ex-hydrotalcite for H2 production by methane decomposition

Hydrogen production free of CO and CO2 was carried out by methane decomposition process using Ni-mixed oxides from hydrotalcite like-materials (ex-HTs) as catalysts. The chemical composition was changed in order to evaluate the influence of the Ni-loading on the main physicochemical (ICP-AES, XRD, XPS, TPR, adsorption/desorption of N2 at 77K and CO2-TPD) properties and on the catalytic performance. For all Ni-loadings (from 7.5 to 58 atomic%), the hydrotalcite structure was the only precursor. After calcination at 850°C, different mixed oxides were formed as a function of Ni-loading, although Ni-Mg-Al mixed oxide matrix or non-stoichiometric spinel phase was the main phase for all catalysts, with the exception of the 58 Ni atomic% sample, in which the NiO segregated from the Mg-Al matrix was the main phase.Methane conversion close to 55% was achieved, hydrogen was the only gaseous product. The most active catalyst was that containing 46% Ni at. Transmission Electron Microscopy (TEM) images of the spent catalysts showed the appearance of multiwall carbon nanotubes (MWCNTs) although under severe reaction conditions, e.g. high temperatures for thermo-programmed temperature experiments, and the long reaction times for isothermal experiments produced low quality MWCNTs.

Preparation, characterization and evaluation of fluoride adsorption efficiency from water of iron-aluminium oxide-graphene oxide composite material

Graphene oxide (GO)-incorporated iron-aluminium mixed oxide (HIAGO) composite, a nobel material was prepared and characterized by FTIR, XRD, TGA/DTA, SEM, TEM, and Raman spectroscopy, which had been employed for adsorption of the fluoride from aqueous solutions. When this material was examined for fluoride scavenging ability from water, it had been established that the as-prepared HIAGO obtained by incorporating 3.0g GO per 0.2 fraction of one gram formula amount of the mixed oxide matrix showed highest fluoride adsorption capacity (qe, mgg−1) at pH∼7.0 and ambient temperature. The material showed an increase of qe with pH up to ∼5.5, and then reduced. Kinetically, fluoride adsorption took place obeying the pseudo-second order model. The Langmuir adsorption isotherm described the equilibrium data best with monolayer adsorption capacities 22.13, 22.90 and 27.75mgg−1 at 288, 308 and 318K, respectively, indicating endothermic nature of adsorption process, which was also confirmed from the thermodynamic analysis of equilibrium data. Fluoride adsorption efficiency of HIAGO had been predicted by modelling a single stage batch adsorber design parameters.

Analysis of safety parameters for the MINERVE reactor

Abstract The present study aims to show the effect of different cross section libraries on MINERVE reactor safety parameters. The MCNP5 calculation model of the MINERVE reactor facility is used to determine core and safety parameters such as axial and radial fission rate distributions, control rod worth and spectral indices. Different neutron spectra were achieved by changing the experimental lattice within the MINERVE reactor. MINERVE provides a large experimental basis for the improvement of the cross section databases. The current study calculates these parameters by MCNP5 code using three different cross section libraries (the continuous energy cross sections of the ENDFB-VI, T16-2003, and ENDF/B-VII.1 libraries). Neutronic calculations were performed for R1UO2, R1MOX, R2UO2, and R2MOX core configurations, representative of a LWR loaded with UO2, mixed oxide matrix, over moderated UO2 and over moderated MOX, respectively. The study aims to determine the most suitable cross section library to be used with MCNP5 reactor calculation code for light water reactor fuel lattice. The MCNP5 results were compared with the experimental results.

Application of manganese (II) phthalocyanine synthesized in situ in the SiO 2/SnO 2 mixed oxide matrix for determination of dissolved oxygen by electrochemical techniques

This work describes the in situ immobilization of Mn(II) phthalocyanine (MnPc) in a porous SiO 2/SnO 2 mixed oxide matrix obtained by the sol gel processing method. The chemically modified matrix SiO 2/SnO 2/MnPc, possessing an estimated amount of 8 × 10 −10 mol cm −2 of MnPc on the surface, was used to prepare an electrode to analyze dissolved oxygen in water by an electrochemical technique. The electrode was prepared by mixing the material with ultrapure graphite and evaluated using differential pulse voltammetry. Dissolved O 2 was reduced at −0.31 V with a limit of detection (LOD) equal to 7.0 × 10 −4 mmol L −1. A mechanism involving four electrons in O 2 reduction was determined by the rotating disk electrode technique.

Au Nanoparticles in Nanocrystalline TiO2−NiO Films for SPR-Based, Selective H2S Gas Sensing

Thin films composed of Au nanoparticles dispersed inside a TiO2−NiO mixed oxide matrix are prepared by the sol−gel method, resulting in nanostructured composites with a morphology and crystallinity that depend on synthesis parameters and thermal treatment. Their functional activity as hydrogen sulfide optical sensors is due to Au-localized surface plasmon resonance (SPR) which is reversible. The detection sensitivity is shown to be down to a few parts per million of H2S, and almost no interference in response is observed during simultaneous exposure to CO or H2, resulting in a highly sensitive and selective sensor for hydrogen sulfide detection. For mechanistic studies, experimental evidence using reaction product analysis and thin film surface characterization suggests a direct catalytic oxidation of H2S over the Au−TiO2−NiO nanocomposite film.

Cobalt–nickel mixed oxide surface: A promising adsorbent for the removal of PR dye from water

A mixed oxide of cobalt (Co) and nickel (Ni) with an approximate composition of Co 0.4Ni 0.4O 0.2 was prepared chemically by precipitating from the corresponding metal carbonates and heating the mixture of carbonates at 650 °C under ambient atmosphere. The mixed (Co–Ni) oxide thus prepared was characterized by IR, SEM and XRD methods. The composition of the mixed metal oxide was obtained by EDX analysis. The surface behavior of the Co–Ni mixed oxide matrix was tested by adsorption studies and pH pzc measurement. The Co–Ni mixed oxide matrix behaves as a charged adsorbent at the pH media higher and lower than its pH pzc value (9.50) and thus found to be capable of anchoring the oppositely charged species onto its surface. Removal of cationic and anionic dyestuffs, viz., methylene blue (MB) and procion red (PR), respectively, was attempted using the mixed oxide surface as adsorbent. Although both the dyes can be removed by the mixed oxide, the extent of PR removal (∼70%) seems to be much higher than that of MB (∼20%) demonstrating the superior performance of the Co–Ni mixed oxide for its use as adsorbent in removing the anionic PR dyestuff from water.

Knoevenagel condensation reaction over acid–base bifunctional nanocrystalline Ce xZr 1−xO 2 solid solutions

Highly thermally stable three-dimensional spongelike mesoporous Ce x Zr 1− x O 2 solid solutions consisting of nanometer size particles with different Ce/Zr compositions were synthesized by a modified sol–gel procedure using a triethanolamine/water mixture as a solvent to be used in liquid Knoevenagel condensation reaction. These materials were investigated in detail by means of X-ray diffraction (XRD), Raman spectroscopy, chemical analysis, X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), UV–Vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and adsorption microcalorimetry. The XRD, HRTEM and XPS studies proved the presence of nanocrystalline Ce x Zr 1− x O 2 solid solutions. These solid solutions showed excellent chemoselectivity in the classical Knoevenagel reaction. The large pore sizes (around 10 nm) highlight the possibility of using Ce x Zr 1− x O 2 as a support material for versatile catalytic systems. The results obtained from NH 3 and SO 2 adsorption microcalorimetry experiments successfully demonstrated the incorporation of ZrO 2 into the CeO 2 lattice resulting in both acidic and basic surface sites in a mixed oxide matrix.

Selective Extraction of Metals from Mixed Oxide Matrixes Using Choline-Based Ionic Liquids

The solubility of a range of metal oxides in a eutectic mixture of urea/choline chloride is quantified, and it is shown that the dissolved metals can be reclaimed from a mixed metal oxide matrix using electrodeposition.

Analytical electron microscopy of the mixed zone in NiCoCrAlY-based EB-PVD thermal barrier coatings: as-coated condition versus late stages of TBC lifetime

The microstructural evolution of the alumina-zirconia mixed zone in a NiCoCrAlY-based electron beam physical vapor deposited (EB-PVD) yttria partially stabilized zirconia (Y-PSZ) thermal barrier coating (TBC) system from the as-coated condition into the advanced stages of TBC lifetime is monitored by analytical transmission electron microscopy (TEM). In the as-coated condition yttria-rich islands at the thermally-grown oxide (TGO)/TBC interface locally impede zirconia uptake of the scale during TBC deposition and give rise to the formation of an “off-plane” alumina-zirconia mixed zone textured perpendicular to the TGO/TBC interface. During prolonged isothermal/cyclic oxidation an increased chromium diffusion through the TGO scale turns the mixed zone into a reaction zone introducing a morphological instability of the mixed zone/TBC interface due to solutioning of the bottom TBC layer.This microstructural pattern is corroborated by a triple-stage growth model for the mixed zone during three successive stages in TBC lifetime: (i) during TBC deposition, the thickness of the mixed zone increases due to predominant outward aluminum diffusion and uptake of zirconia. No columnar alumina zone (CAZ) has formed at this stage, (ii) upon completion of the transition alumina-to-corundum phase transformation the thickness of the mixed zone remains constant while the change in diffusion mechanism for an inward oxygen diffusion process now initiates parabolic growth of the columnar alumina sublayer of the TGO scale, (iii) in the late stage of TBC lifetime an marked outward chromium diffusion from the bond coat causes the mixed zone to resume growth due to TBC destabilization and the formation of a (Al, Cr)2O3 mixed oxide matrix phase.A transient YCrO3 phase is proposed for driving the destabilization of yttria-rich sections of the bottom TBC layer.

Microstructure of irradiated SBR MOX fuel and its relationship to fission gas release

Abstract SEM and EPMA examinations of the microstructure and microchemistry of British Nuclear Fuel’s quasi-homogeneous SBR MOX fuel following irradiation suggests behaviour which is very similar to that observed in UO2. Most significantly, a fission gas release of 1% in three-cycle SBR MOX PWR rods is associated with the development of a well-defined intergranular bubble network, which has not been seen previously in the more heterogeneous MOX fuels irradiated under similar conditions. The contrast between the observations is attributed to the relatively low volume fraction and small size of the Pu rich inhomogeneities in the SBR fuel which generate only 4% of the total fission gas and eject most of this into the surrounding mixed oxide matrix. The resulting perturbation in the Xe distribution has a negligible influence on the evolution of the microstructure. A key observation is made from the results of recent post-irradiation annealing experiments performed on SBR MOX and UO2. These confirm near identical fission gas behaviour in the two fuel types when the influence of thermal conductivity and rod rating are removed.

Structure and photoluminescence properties of sol–gel TiO 2–SiO 2 films

TiO 2–SiO 2 films (Ti/Si=1:1) have been prepared by the sol–gel method. The structure and photoluminescence (PL) properties of the films heat-treated at different temperatures have been investigated. The films appear composed of TiO 2 nanocrystallites in anatase form embedded in SiO 2-rich matrix. Emission bands are observed in all the heat-treated films. This PL is attributed to various defects resulting from thermal treatment and crystallization of TiO 2 and to energy levels in the mixed oxide matrix.

A TEOM-MS study on the interaction of N 2O with a hydrotalcite-derived multimetallic mixed oxide catalyst

The interaction of N 2O with a multimetallic mixed oxide (ex-Co,Mg-Rh,Al-HTlc), prepared via calcination of a hydrotalcite-like compound, has been studied employing a tapered element oscillating microbalance coupled to a mass spectrometer (TEOM-MS), capable of simultaneous recording of mass and gas-phase composition variations during the process. The study is based on step–response experiments (SRE) carried out at different temperatures, ranging from 303 to 598 K. The observed mass variations are related to the amount of adsorbed species under reaction conditions and their stability. The gas analysis gave simultaneous information on the rate of N 2O decomposition and the steady-state condition. Based on the results obtained and literature data, an interaction model of N 2O with the mixed oxide, including the exchange of the adsorbed oxygen with the catalyst lattice oxygen, is proposed. At low temperatures (303 K) molecular adsorption of N 2O is also considered. The experimental time- and temperature-dependent mass variations can be well described. Oxygen recombination/desorption and oxidation of the surface sites appeared to be the slowest processes, while the removal of adsorbed oxygen by N 2O from the gas phase was much faster. Activation energies of the steps involved range between 16 and 40 kJ/mol. The observed mass changes are mainly attributed to the Co in the mixed oxide matrix.

Highly Dispersed Phosphate Supported in a Binary Silica−Titania Matrix: Preparation and Characterization

Titanium phosphate supported in a mixed oxide matrix was prepared by reacting SiO2/TiO2, obtained from the sol−gel process, with phosphoric acid. HPO42- is the species present in the matrix, and it is immobilized by the Ti−O−P bond on the surface. The titanium phosphate is highly and homogeneously dispersed in the SiO2/TiO2 matrix, with the domain of titanium oxide particles about 1 nm, estimated from the UV absorption band threshold. The specific surface areas, determined by the BET multipoint method, changed between 397 and 755 m2 g-1 and the average pore volumes between 0.38 and 0.63 mL g-1 for samples prepared with different contents of titanium phosphate. The titanium hydrogenphosphate is thermally very stable and showed a high proton exchange capacity between 0.50 and 1.10 mmol g-1.

The conductivity of oxide cathodes. Part 16: Thermodynamic considerations of matrix stability

Under conditions of free evaporation in vacuo from a platinum substrate the sublimate from barium oxide is almost wholly oxide, whereas that from strontium oxide is a mixture containing a high proportion of metallic strontium. The present Part suggests that this difference in behaviour can be explained in terms of the energy difference between the heats of formation and sublimation of the two oxides. This hypothesis predicts that both calcium oxide and magnesium oxide should behave in a manner similar to strontium oxide, and experiments show that the prediction is correct. A further prediction suggests that barium oxide should itself behave like the other three alkaline-earth oxides if its evaporation is physically restricted, and this again turns out to be demonstrable. The hypothesis is finally used to provide a satisfactory explanation for the emission of excited strontium-metal vapour from a mixed-oxide matrix under heavy current loading.