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Nanocrystalline cobalt spinel has been recognized as a very active catalytic material for N2O decomposition. Its catalytic performance can be substantially modified by proper doping with alien cations with precise control of their loading and location (spinel surface, bulk, and spinel-dopant interface). Various doping scenarios for a rational design of the optimal catalyst for low-temperature N2O decomposition are analyzed in detail and the key reactivity descriptors are identified (content and topological localization of dopants, their redox vs. non-redox nature and catalyst work function). The obtained results are discussed in the broader context of the available literature data to establish general guidelines for the rational design of the N2O decomposition catalyst based on a cobalt spinel platform.

Ceramic open cell foams (OCF) are characterized by lower pressure drop, high geometric surface area, and enhanced radial convection in comparison with monolith-type supports. In this work, silicon carbide (SiC) and zirconia (Zir) OCF with different pore per inch (ppi) density were coated with 200 mg of Co3O4 by solution combustion synthesis and doped with 3 wt % of Pd via wetness impregnation. Their catalytic activity was tested toward the lean oxidation of methane at different weight hourly space velocities. Zir OCF with 30 ppi exhibits the best catalytic activity for all reacting conditions, followed by Zir 45 ppi, SiC 45 ppi, and SiC 30 ppi. The better performance of Zir OCF was rationalized considering their lower volumetric heat exchange coefficients, which favor the reaction heat removal by convection via the flue gases. A 200 h stability test on the best structured catalyst demonstrated full methane conversion at a temperature below 400 °C. These results confirm the fundamental role of thermal cond...

A series of Pd/Co 3 O 4 catalysts with increasing palladium loading in the range of 0.5–5 wt.% was prepared by incipient wetness impregnation of Co 3 O 4 . Solution combustion synthesis with urea as a fuel was used to optimize the Co 3 O 4 reactive support for palladium in the combustion of methane in lean conditions. The obtained catalysts were thoroughly examined by XRD, XPS, XRF, RS, FESEM, H 2 -TPR, TGA, and N 2 -BET techniques. The catalytic tests of CH 4 combustion were performed for 0.5, 1, and 2 vol.% CH 4 , with constant lambda value. The obtained results revealed that a sub-stoichiometric fuel-to-oxidizer ratio, 0.75, results in the most catalytically active Co 3 O 4 phase. The important differences in the catalysts’ activity were apparent for the highest CH 4 concentration, with the 3% Pd/Co 3 O 4 being the most active catalyst. The observed activity was explained considering the physicochemical, spectroscopic, and microscopic characterization of the catalysts with the PdO nanocrystals surface distribution being the determining factor for the catalysts’ reactivity. A simple model accounting for the observed dispersion effect is proposed. The model is based on a two types of the interaction of the surface PdO active phase with the Co 3 O 4 support. Firstly, cobalt oxide helps to remove hydroxyl species from the PdO surface, thus making the active sites more available for methane activation. Secondly, cobalt spinel provides lattice oxygen to the PdO phase, again helping to recreate active sites thereon.

In this work a series of mixed iron-cobalt spinel catalysts was synthesized by solution combustion synthesis and doped with 3 wt% of palladium via incipient wetness impregnation. The catalysts were synthesized with different Co:Fe ratios, characterized from the structural and surface point of view (XRD, XRF, μRS, BET, FESEM), and tested toward the oxidation of methane in lean conditions, in gas mixtures containing from 0.5 to 2 vol% of CH4. The temperature window for the catalytic activity of the undoped mixed iron–cobalt spinels spread from 350 to 650 °C. While lower iron substitution levels lead to a decrease in the spinel’s activity, the catalyst with 2/3 of the cobalt in the Co3O4 substituted with iron shows similar activity to the parent Co3O4. Although the materials were proved to be heterogeneous from the crystal phase point of view (a mixture of cobalt–iron spinels), the observed reactivity still depends on the amount of iron introduced during the synthesis. The addition of Pd lowered the temperature window for the catalytic activity to the range of 250–550 °C. The promoting effect of Pd is most evident for the pure Co3O4 catalyst. In contrast to the Pd-free catalysts, the best activity of Pd-promoted samples was observed for the catalysts with the highest iron content.

In this work, a series of Co3O4 spinels were produced by different synthesis routes (precipitation, solution combustion synthesis, and hard template method), and were used as non-noble catalysts for the oxygen evolution reaction (OER) under basic conditions. The investigated catalysts have a proportional relation between electrochemical activity, surface roughness, and specific surface area. The hard template synthesis method resulted in the most active catalyst compared in this work, which we ascribe to its highly porous structure, and concomitant Co3+/Co4+ redox couple at a lower potential, attributed to the OER. The most performant catalyst was compared with a commercial catalyst (Ni@NiO, Alfa Aesar) showing only 0.01 V overpotential difference, evaluated at 10 mA cm− 2 (overpotential 0.44 V).

Series of precursors was prepared by precipitation of cobalt nitrate in aqueous solutions using various precipitation agents (NH3·H2O, NaOH, Na2CO3) and reactions conditions (OH/Co molar ratio, aging time). Powder XRD showed different phase composition of the obtained precursors, in which β-Co(OH)2, CoII–CoIII layered double hydroxide, and basic cobalt carbonate were identified. Only Co3O4 spinel-like oxide was found in products after heating at 500 °C in air but different N2O conversions were observed over the examined oxide catalysts. Especially the catalysts obtained from β-Co(OH)2 precursors showed high catalytic activity in N2O decomposition. The correlation between methods of preparation, phase composition of precursors, catalytic properties of the related oxide catalysts, and the role of the cobalt ions as catalytic active sites is discussed.

Cobalt spinel catalysts promoted with different cesium loadings from various precursors (Cs2CO3, CsNO3, CH3COOCs, and CsOH) were prepared by incipient wetness impregnation. The catalysts were characterized by XRF, XRD, SEM, XPS and Raman Spectroscopy. The work function studies were used to optimized the surface doping and monitor the retention of surface oxygen. The stability of cesium promoter was evaluated by means of species resolved – thermal alkali desorption method. The catalytic activity of N2O decomposition over the synthesized catalysts was studied by temperature programmed reaction. The role of cesium precursor was evaluated in terms of dispersion and the nature of the counterion. The results show that the most active deN2O catalysts are obtained for cesium carbonate at the narrow loading range of 2–3 atoms/nm2 (complete N2O conversion at T < 200 °C). The twofold promotional effect is discussed in terms of modification of the electronic properties of the spinel catalyst (stimulation of dissociation step: N2O + e = N2 + O–) and stability of the surface oxygen species (recombination step: O– = ½O2 + e).

Blue spinel crystals in the MgAl2O4-CoAl2O4 series: II. Cation ordering over short range and long range scales

Ferrimagnetic nanoparticles of CoFe2O4 with dimensions of 4-16 nm were synthesized by pyrolysis of a mixture of acetylacetonates of iron and cobalt. In the temperature range 300-500 K investigated field dependence of magnetization up o 18 kOe. Found a significant contribution of "surface" anisotropy to the effective anisotropy of the nanoparticles. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35365

El electrodepósito es una técnica que permite la obtención de óxidos metálicos nanoestructurados de Co3O4 y RuO2 en intercapas sobre soportes de titanio. Estos composites soportados sobre titanio presentan propiedades electrocatalíticas superiores a las de materiales obtenidos por otras técnicas clásicas como sol-gel o impregnación seguida de descomposición térmica. La actividad electrocatalítica para la generación de oxígeno es determinada mediante voltametría cíclica y el aumento de la conductividad a potenciales más anódicos mediante espectroscopía de impedancia electroquímica (EIS). Las técnicas Raman, DRX, SEM y EDX son utilizadas para la caracterización estructural de los óxidos. The electrodeposit is a technique that allows the production of nanostructured metal oxides of RuO2 and Co3O4 in interlayers on titanium supports. That titanium supported composite electrodes have better electrocatalytic properties than materials obtained by other classic techniques such sol- gel or impregnation followed by thermal decomposition. The electrocatalytic activity for oxygen evolution is determined by cyclic voltammetry and the conductivity increased to more anodic potentials by electrochemical impedance spectroscopy (EIS). Raman, XRD, SEM and EDX techniques are used for structural characterization of the oxides.

La electrólisis es una alternativa eficiente para oxidar los compuestos responsables del color de los vertidos acuosos de la industria textil, como son los compuestos del tipo azo. El material del cual está fabricado el electrodo y el pH de la disolución han sido identificados como determinantes en la obtención de la máxima eficiencia en corriente. En este estudio se realizó la oxidación electroquímica del anaranjado de metilo: 4-(4’- dimetilaminofenilazo) bencensulfonato de sodio, utilizando electrodos de espinela de cobalto, dióxido de plomo y grafito, en solución de cloruro de sodio a diferentes valores de pH. The electrolysis is an efficient alternative to oxidize the compounds responsible for the color of the textile industry waste waters, like the azo compounds. The material of which is manufactured the electrode and the pH of the solution has been identified as decisive to reach the maximum current efficiency. In this study, the electrochemical oxidation of the methyl orange: sodium 4-(4’- dimethylaminophenylazo) benzensulfonate, was carried out using cobalt spinel, lead dioxide and graphite electrodes, in a sodium chloride solution at different pH values.

Mullite, 3Al2O3*2SiO2, is attractive ceramic material for advanced applications. Variety of mullite matrix composites have been recently studied. The aim of the work was to examine in situ formation of spinell-mullite composites by sol-gel synthesis of diphasic gels doped with 1, 2 and 3 at.%, Co2+ (introduced on account of aluminium). The gels were prepared by mixing Al and Co nitrate water solutions with tetraetoxysilane, dissolved in ethanol. The structural evolution with temperature has been studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Rietveld structure refinement. The microstructure and morphology has been investigated by scanning electrion microscopy (SEM) and energy dispersive X-ray spectrometry (EDX). DSC analyses provide two exothermic effects, the first attributed to the spinel crystallization around 1000C, and second caused by the mullite crystallization at higher temperatures. Shift of peaks towards lower temperatures with the increase of Co2+ content has been observed. At lower taemperaturtes XRD patterns show no distinction between Co and Al-Si spinels, while sperate diffraction lines could be spotted at 1350C. SEM micrographs of samoples thermally treateed at these temperatures revealed the presence of particles with different morphology: fewer coarser particles embedded in nano-sized mullite matrix. Using EXD analises it was determined that cobalt is concentrated in coarser particles while matrix is composed of alumosilicate phase. At 1650C samples are composed of mullite, Co-spinel and traces of alpha-alumina. The differences in the mullite lattice parameters between samples could be the consequence of cobalt entering the mullite structure, on the other hand, they could be explained by variations in Al2O3 to SiO2 ratio. Rietveld analyses of the sample with 3% Co2+ indicated that the majority of Co2+ is in spinel phase. The kinetic analysis showed certain decrease in activation energy for mullite crystallization in comparison with non-doped sample.