Aqueous Solution Of Cobalt Nitrate Research Articles

Synthesis and Characterization of the Catalysts 5 wt.% and 10 wt.% Co/SBA-15

Catalysts supported on SBA-15 were obtained by wet impregnation using aqueous solution of cobalt nitrate, where different contents of cobalt (5 wt% and 10 wt%) were prepared. The molecular sieve SBA-15 was synthesized using tetra ethyl ortho silicate (TEOS) as silicate source, and triblock copolymer, poly-(ethylene oxide)-poly (propylene oxide)-poly-(ethylene oxide) PEO-PPO-PEO as the organic structure directing agent. These materials were characterized by X-ray diffraction (XRD), X-ray energy dispersion spectrophotometer (EDX) and Nitrogen adsorption–desorption isotherms (BET). The results from the XRD showed that the molecular sieve mesoporous (SBA-15) was identified by X-ray diffraction, especially from the (210) and (300) peaks, which represent a typical spectrum for the SBA-15. Characterization of catalysts by Nitrogen adsorption–desorption isotherms (BET) made it possible to verify the the samples had been of type IV with hysteresis of corresponding the H2 type the porous materials.

Study on the steam reforming of ethanol over cobalt oxides

A high valence cobalt oxide, CoO x , was prepared from a cobalt nitrate aqueous solution through precipitation with sodium hydroxide and oxidation by hydrogen peroxide. Furthermore, pure nanocrystalline cobaltic oxide (Co 3O 4) particles were obtained from the CoO x by calcination at 300, 500 and 700 °C (labeled as C300, C500 and C700, respectively). All samples were characterized by X-ray diffraction (XRD), Raman spectroscopy and temperature-programmed reduction (TPR). Their catalytic activities toward steam reforming of ethanol (SRE) were tested in a fixed-bed reactor. The results showed that the phase components were transferred upon the treatment temperature, i.e., the CoO x exhibited mainly CoO(OH), C300, C500 and the C700 exhibited Co 3O 4. The as-prepared CoO x catalyst under low temperature possessed high activity. The best yield of hydrogen ( Y H 2 ) approached the theoretical value around 375 °C. Under H 2O/EtOH molar ratio of 13 and 22,000 h −1 gas hourly space velocity (GHSV) for the as-prepared CoO x catalyst, the Y H 2 arrived 5.72 and only minor CO (<2%) and CH 4 (<0.8%) were detected.

Cobalt oxide supported on alumina catalysts prepared by various methods for use in catalytic afterburner of PEM fuel cell

In the present work we have investigated the influence of the preparation method on the physicochemical and activity features of CoO x /γ-Al 2O 3 catalysts used for the combustion of anode tail gas produced in a proton-exchange membrane (PEM) fuel cell. The catalysts prepared contain 21% (w/w) Co and have been calcined at 850 °C. Three different impregnation methodologies have been followed: incipient wetness impregnation (IWI) using a cobalt nitrate aqueous solution, incipient wetness impregnation using a mixed cobalt nitrate–nitrilotriacetic acid (IWI-nta) aqueous solution and equilibrium deposition filtration (EDF) using a cobalt nitrate aqueous solution. The catalysts were characterized using nitrogen adsorption for determining the specific surface area, the pore volume and the mean pore diameter as well as using X-ray powder diffraction (XRD), diffuse reflectance spectroscopy (DRS; UV–vis), LRS, X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR). Catalytic activity measurements were performed in the temperature range 250–850 °C using a continuous flow fixed-bed micro-reactor working under atmospheric pressure and fed with a reaction mixture consisted of 15% H 2/3% CO/1.1% CH 4/20% O 2 balanced in He. The EDF methodology imposed interfacial deposition and resulted to the formation of an almost bi-dimensional surface precipitate. Upon calcination, this surface precipitate provided a very well-dispersed CoO x amorphous species strongly interacted with the support surface and thus hardly reducible as well as relatively small Co 3O 4 supported nanocrystals (14.3 nm). The first phase is the predominant one. Therefore, EDF resulted to a catalyst with the highest cobalt surface and specific surface area. The conventional IWI imposed bulk (solution) precipitation and thus induced relatively large supported crystallites which upon calcination provided relatively large supported Co 3O 4 nanocrystals (19.8 nm) and CoAl 2O 4 as well. The formation of the relatively large nanocrystals and the insertion of cobalt inside the γ-alumina lattice to form CoAl 2O 4 may be responsible for the lowest cobalt surface obtained in this catalyst. The presence of the nitrilotriacetic acid in the impregnating solution induced the exchange of the water ligands of the Co(II) aqua complex present in the cobalt nitrate solution with organic ligands and thus the bulk precipitation of an organometallic complex. The more bulky organic ligands decreased the cobalt-support interactions. Thus, the insertion of cobalt inside the γ-alumina lattice and the formation of CoAl 2O 4 are inhibited upon calcination of the IWI-nta sample. This may be responsible for the relatively higher cobalt surface obtained with respect to that achieved in the IWI sample though the size of the Co 3O 4 nanocrystals is larger in the IWI-nta sample (25.8 nm). At relatively high reaction temperatures all catalysts exhibited almost the same activity for oxidation reactions. In contrast, at low reaction temperatures the EDF catalyst proved to be more active for the CH 4 production as well as for the oxidation of H 2 and CO. This behaviour may be attributed to the favourable physicochemical characteristics of this catalyst.

Al-substituted α-cobalt hydroxide synthesized by potentiostatic deposition method as an electrode material for redox-supercapacitors

Al-substituted α-cobalt hydroxide was prepared by a potentiostatic deposition process at −1.0 V (vs. Ag/AgCl) onto stainless steel electrodes by using a mixed aqueous solution of cobalt nitrate and aluminum nitrate. Their structure and surface morphology were studied by using X-ray diffraction analysis, energy dispersive X-ray spectroscopy and scanning electron microscopy. The SEM images showed changes in the nanostructure of α-cobalt hydroxide by the addition of Al. Galvanostatic charge–discharge curves showed a drastic improvement in the capacitive characteristics of α-cobalt hydroxide, with a specific energy increase from 11.3 to 18.7 Wh kg −1 by the substitution of just 8 at.% Al, and a specific capacitance of 843 F g −1 between 0 and 0.4 V. The cycle stability data suggest no significant changes in the discharge characteristics of α-cobalt hydroxide by the addition of Al.

Preparation and catalytic performance of Co3O4 catalysts for low-temperature CO oxidation

Without use of any surfactant or oxidant, a series of Co3O4 catalysts have been prepared from cobalt nitrate aqueous solution via a very simple liquid-precipitation method with ammonium acid carbonate followed by calcination at various temperatures. The catalytic performance of the Co3O4 for CO oxidation has been studied with a continuous flowing laboratory microreactor system. The results show that the CO conversion of all the samples can reach 100% at ambient temperature. The catalyst calcined at 300 °C is able to maintain its activity for CO complete oxidation more than 500 min at 25 °C and about 240 min even at −78 °C. High reaction temperature results in a high catalytic stability, while the catalytic stability decreases with further increasing the reaction temperature. Characterizations with X-ray powder diffraction and transmission electron microscopy suggest that all the samples exist as a pure Co3O4 phase with the spinel structure, the samples are apt to aggregate and the specific surface area gradually decreases with increasing the calcination temperature, which directly leads to the decrease of catalytic stability. Furthermore, the amount of active oxygen species measured by CO titration experiments appears to be critical for catalytic performance.

Catalysts based on Co/zirconium doped mesoporous silica MSU for the hydrogenation and hydrogenolysis/hydrocracking of tetralin

Zirconium doped mesoporous silica (MSU) has been used as a support of Co catalysts with different Co-loadings. These catalysts have been characterised by several techniques such as XRD, XPS, textural properties, H 2-TPR, NH 3-TPD, chemisorption of H 2, DRIFTS and FT-IR of adsorbed NO. The performance in the hydrogenation and hydrogenolysis/hydrocracking of tetralin at different temperatures has been examined in a high-pressure fixed-bed continuous-flow stainless steel catalytic reactor operating at 6.0 MPa of pressure. The incorporation of cobalt by using the incipient wetness method with an aqueous solution of cobalt nitrate is effective for preparing catalysts with 5–20 wt.% Co. The behaviour of these catalysts demonstrates that the higher the metallic loading, the contact time between catalyst and reactants, and the H 2/tetralin molar ratio, the better the results with conversions in the steady-state near to 100% and better the yields of hydrogenation and hydrogenolysis/hydrocracking products. Thus, the catalyst with 15 wt.% of Co, operating at 315 °C, with a contact time of 3.6 s and an H 2/tetralin molar ratio of 15, gives rise to a conversion of tetralin of nearly 100%, yields of hydrogenation of 71%, and of hydrogenolysis/hydrocracking of 28% after 6 h on-stream. In addition, the thiotolerance of these catalysts has been tested with a feed of 425 and 850 ppm of dibenzothiophene (DBT). With 425 ppm of DBT, the performance of the best catalyst is only reduced by 17% after 5 h on-stream. However, with 850 ppm of DBT, a dramatic decrease in the activity is observed, although this activity can be recovered after new thermal and reduction treatments.

Structural and magnetic characteristics of cobalt ferrite-coated nano-fibrous γ-Fe 2O 3

The presence of mesopores in γ-Fe 2O 3 is a limiting factor for its optimal magnetic properties. Therefore, high coercive γ-Fe 2O 3 nano-fibrous particles are obtained by coating cobalt ferrite on the surface. An aqueous solution of cobalt nitrate+ammonium ferrous sulphate (in the ratio 1:2) precipitated at pH>12.5 in the presence of uniformly dispersed γ-Fe 2O 3 yields cobalt ferrite coating on the surface of the particles at ∼90°C. The nature of the coating, studied by X-ray diffraction and high-resolution electron microscopy (HREM), reveals the epitaxial growth of the CoFe 2O 4 layer on γ-Fe 2O 3 provided the extent of coating ( X Co) is maintained ⩽30 wt%. The pores within the γ-Fe 2O 3 particles are coherently filled up as deciphered by the continuity in the HREM lattice fringes. The surface characteristics using X-ray photoelectron spectroscopy analysis further confirm the coherent coating of cobalt ferrite onto the γ-Fe 2O 3 surface. Studies of cobalt ferrite-coated samples by Mössbauer spectra clearly reveal the hyperfine field characteristics of γ-Fe 2O 3 notwithstanding the CoFe 2O 4 coating at lower contents. As the thickness of the coating increases (∼30 wt%), the spectrum consists of two overlapping sextets (one from the average hyperfine pattern of γ-Fe 2O 3 and A-site of CoFe 2O 4 and the second from the B-site in the bulk CoFe 2O 4). The deposition of CoFe 2O 4-rich surface layer results in an increase in the coercive field ( H c=585 Oe for X Co=10 wt%; H c=1100 Oe for X Co=30 wt%), which is attributed to the formation of uniaxial anisotropy under the influence of the field created by the magnetization of the particles. Saturation magnetization (σ s) also increases from 74.4 emu/g (uncoated) to ∼78.6 emu/g ( X Co=30 wt%) with the extent of coating. In comparison, for Co-substituted nano-fibrous γ-Fe 2O 3 the presence of homogeneously distributed Co 2+ ions (10 at%) enhances the H c (609 Oe) as a result of high magnetocrystalline anisotropy accompanied by shape anisotropy, whereas, σ s decreases (∼60 emu/g) due to the relaxation of spins on the surface atoms of slender particles with mesopores as revealed by Mössbauer spectroscopy for Co 2+-substituted γ-Fe 2O 3.

Synthesis, Characterization and Catalytic Oxidation of Carbon Monoxide over Cobalt Oxide

A mix-valenced cobalt oxide, CoOx, was prepared from cobalt nitrate aqueous solution through a precipitation with sodium hydroxide and an oxidation by hydrogen peroxide. Further, other pure cobalt oxide species were refined from the CoOx by temperature-programmed reduction (TPR) at 170, 230 and 300 °C (labeled as R-170, R-230 and R-300, respectively). They were characterized by X-ray (XRD), infrared (IR), thermogravimetry (TG) and TPR. The major composition of CoOx is CoO(OH), with a small amount of Co4+ species; R-170 is CoO(OH) with a hexagonal structure; R-230 is Co3O4 with a spinel structure and R-300 is CoO with a cubic structure. Their catalytic activities toward the CO oxidation were further studied in a continuous flow microreactor. The results indicated that the relative activity decreased significantly with the oxidation state of cobalt, i.e., CoO(+2)≳Co3O4(+8/3)≫CoO(OH)( +3)≳CoOx(>+3).

In situ FTIR study of cobalt oxides for the oxidation of carbon monoxide

A high-valance cobalt oxide, CoO x , was prepared from cobalt nitrate aqueous solution through precipitation with sodium hydroxide and oxidation by hydrogen peroxide. Further, other pure cobalt oxide species were refined from the CoO x by temperature-programmed reduction (TPR) to 170, 230 and 300 °C. They were characterized by TPR and X-ray diffraction (XRD). Adsorption of CO and the co-adsorption of CO/O2 over the cobalt oxides were further tested by in situ FTIR. It was shown that Co3O4 is quite active for the oxidation of CO at room temperature in the presence of oxygen, leading to the formation of CO2. The variation in the oxidation of CO was interpreted with a mechanism involving two kinds of oxygen species, i.e., *-O2 on the CoO x surface and *-OL on the surface of Co3O4 spinel structure.

Promoting Synergy in CoW Sulfide Hydrotreating Catalysts by Chelating Agents

Adding chelating agents such as 1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid (CyDTA) and triethylenetetraaminehexa acetic acid (TTHA) to the aqueous solution of cobalt nitrate and ammonium metatungstate used for impregnating the silica support results in enhanced activities for the hydrodesulfurization of thiophene after the catalysts have been sulfided. These chelating agents serve to retard the sulfidation of cobalt with respect to that of tungsten, which facilitates the formation of a phase in which Co atoms decorate the edges of WS2, analogous to the well-known CoMoS phase.

Preparation and characterization of uniformly coated particles by homogeneous precipitation (cobalt compounds on nickel compounds)

Abstract Nickel basic carbonate [NiCO 3 · Ni(OH) 2 · H 2O] particles were coated with crystalline cobalt carbonate (CoCO 3) by heating their suspension in an aqueous solution of cobalt nitrate and urea at elevated temperatures. In the absence of core particles, the same reactant mixture produced a dispersion of amorphous cobalt basic carbonate [2CoCO 3 · Co(OH) 2 · H 2O] particles. On calcination at 700°C, the shell and core materials of the coated particles transformed, respectively, into Co 2O 3, and NiO, while producing a third phase (NiCo 2O 4) at the core/coating interface. No sintering was observed during calcination and the particles retained their morphological features to a significant extent.

Electrocatalysis of oxygen evolution at stainless steel anodes by electrosynthesized cobalt hydroxide coatings

Controlled growth of cobalt hydroxide coatings (1–2 μm thick) on stainless steel electrodes was achieved by electrogeneration of base by cathodic reduction of aqueous cobalt nitrate solutions. These coatings catalyse the oxygen evolution reaction in alkaline medium (1 M KOH) by as much as 100 mV, making cobalt hydroxide a candidate catalyst for these applications.

Preparation and characterization of a higher cobalt oxide

The present paper describes the synthesis of a higher cobalt oxide system obtained from a solution technique. Low-temperature cobalt oxide system has been prepared by the reaction of sodium hydroxide and NaOCl with a cobalt nitrate aqueous solution. The composition of solid phase obtained under certain conditions is investigated by X-ray, IR, XPS- and atomic absorption spectral analyses, magnetic measurements and chemical analysis. The results obtained show that a Co oxide system may be achieved, in which Co ions are mainly in the highest oxidation state (+ 4) and in octahedral coordination. The proposed method leads to the obtaining of highly active low-temperature catalysts for oxidation of toxic substances (phenols, alcohols, aldehydes, CN − and S 2−) in an aqueous medium in the absence of gaseous phase oxygen.

Electrochemical synthesis of α-cobalt hydroxide

R. S. Jayashree and P. Vishnu Kamath, J. Mater. Chem., 1999, 9, 961 DOI: 10.1039/A807000H

Effects of Ethanol Impregnation on the Catalytic Properties of Silica‐Supported Cobalt Catalysts

AbstractSilca‐supported Co3O4 (6 wt% as Co) catalysts were prepared by pore volume impregnation of ethanol or aqueous cobalt nitrate solutions, and calcined in vacuo to 300 °C. The catalytic performances of these catalysts for oxidation and hydrogenation of CO were examined. All Co3O4/SiO2 catalysts were found to be very active in catalyzing oxidation of CO to CO2 as compared to a commercial 1 wt% Pt/Al2O3. The ethanol‐prepared catalysts exhibited higher activity than those of the aqua‐prepared catalysts. Pre‐calcination of the ethanol‐prepared catalysts in oxygen at 600 °C resulted in a dramatic decrease in the activity. Temperature programmed oxidation indicated the presence of carbon deposits on the surface of used catalysts. Infrared spectra showed the continuous generation of CO2 when these catalysts were exposed to CO. These indicate the primary role of CO disproportionation in catalytic oxidation of CO on Co3O4 at low temperature and explain the sharp decrease in activity in the initial period. After reduction at 400 °C, the ethanol‐prepared catalysts were also found to be more active in catalyzing hydrogenation of CO, and produced less methane and olefin (C2‐C4) fraction. Higher turnover frequencies were observed after high temperature reduction (600 °C) as well, at which ethoxyl groups were removed from silica surface. In both reactions, the enhanced activity for the ethanol‐prepared catalysts can not be fully accounted for by the increase in the dispersion of Co3O4 or CO metal. This suggests that the surface structures of Co3O4 or CO were further modified by the carbonaceous species derived from ethanol.

Effects of Ethanol Impregnation on the Properties of Silica-Supported Cobalt Catalysts

Silica-supported cobalt (6 wt%) catalysts were prepared by pore volume impregnation of either ethanol or aqueous cobalt nitrate solutions on calcined silica (500 and 1000°C), and characterized by infrared, hydrogen chemisorption, thermogravimetry–mass spectroscopy (TG-MS), and X-ray diffraction (XRD). XRD and TG show that the main cobalt phase is Co3O4(above 90%) after calcinationin vacuoto 300°C. The influence of the calcination temperature of silica on the particle size of Co3O4is not significant. Smaller Co3O4crystallites and more Co–SiO2interaction species were obtained when catalysts were prepared with ethanol instead of aqueous solution. In addition, ethoxyl groups were formed on the silica surface with a surface density of 0.17 to 0.09 ethoxyls/nm2depending on the calcination temperature of the pretreated silica. The decrease in Co3O4crystallite size on ethanol impregnation is attributed to the presence of surface ethoxyls which might hinder the aggregation of Co3O4during its formation from the thermal decomposition of cobalt nitrate. As a consequence, a larger percentage dispersion of cobalt metal was obtained after reduction at 400°C. TG-MS results showed that ethoxyl groups were decomposed into ethylene in the temperature range 500–600°C in He or H2. Hence, ethoxyl groups might affect the sintering process of the cobalt metal during reduction as well.

Low-temperature cobalt oxide as rechargeable cathodic material for lithium batteries

The present paper describes a novel synthesis of LiCoO 2 obtained from a solution technique. Low-temperature LiCoO 2 compound has been prepared by the reaction of lithium and ammonium hydroxyde with a cobalt nitrate aqueous solution. An appropriate heat treatment of the corresponding precipitate performed at 400 °C in air leads to a crystallized layered LiCoO 2. Preliminary structural and electrochemical experiments are reported and evidenced that lithium extraction occurs at a lower potential (3.7 V) than for its high-temperature analogue with a maximum depth of charge of 0.5 Li Co when used in a conventional electrolyte.

Zeolite-supported cobalt catalysts for the conversion of synthesis gas to hydrocarbon products

Three differently prepared cobalt/ZSM-5 catalysts were investigated with respect to physical and chemical properties and to activity and selectivity for conversion of synthesis gas. The catalyst preparations consisted of the following: (1) direct decomposition of C/sub 5/H/sub 5/Co(CO)/sub 2/ on ZSM-5, (2) impregnation of ZSM-5 with an aqueous solution of cobalt nitrate, and (3) physical admixture of precipitated cobalt oxide with ZSM-5. At about 3 wt % cobalt loading, the first catalyst showed higher dispersion, higher (H/sub 2/ + CO) conversion, and about 10 times higher yield of gasoline-range hydrocarbons (g/h) than the catalyst prepared by the other two methods. Some H/sub 2/ and CO chemisorption studies and magnetization measurements were conducted to measure the average particle diameter. Infrared studies of chemisorbed pyridine of these samples indicate that ion exchange of Co/sup 2 +/ for acidic protons occurs in organometallic-impregnated and aqueous solution-impregnated catalysts. 18 references, 6 figures, 4 tables.