Aqueous Solution Of Cobalt Nitrate Research Articles

Direct growth of hierarchical CoFe2O4 flower-like nanoflake arrays on Ni foam for high performance asymmetrical supercapacitor

• Tulip-like iron microstructure was electrodepositied on Ni foam from suspension of Fe 2 O 3 . • Fe@Ni foam was hydrothermally converted into CoFe 2 O 4 /Ni foam in solution of Co 2+ . • Hierarchical flower-like CoFe 2 O 4 nanoflake arrays exhibits excellent electrochemical properties. • ASC assembled with CoFe 2 O 4 /Ni foam and AC demonstrates capacitive performances. Flower-like cobalt ferrite (CoFe 2 O 4 ) nanflake arrays with high mass-loading was directly grown on Ni foam with a facile two-step hydrothermal method. First, hierarchical tulip-like Fe microstructure was electrodeposited on Ni foam from an alkaline Fe 2 O 3 suspension. Then, CoFe 2 O 4 flower-like CoFe 2 O 4 nanoflake arrays on Ni foam (CoFe 2 O 4 /Ni foam) was produced by heating Fe-modified Ni foam in cobalt nitrate aqueous solution containing low concentration of copper sulfate. The CoFe 2 O 4 /Ni foam was characterized with scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-Ray spectroscopy (EDS) and Brunauer-Emmett-Teller gas sorptometry measurements (BET). The electrochemical performances of CoFe 2 O 4 /Ni foam were tested with cyclic voltammetry (CV), galvanostastic charge/discharge technique (GCD) and electrochemical impedance spectroscopy (EIS). As capacitive electrode, CoFe 2 O 4 /Ni foam exhibits high areal capacity (9.7C cm −2 at 10 mA cm −2 ), good columbic efficiency (97.25% at 10 mA cm −2 ) and excellent cycling stability (capacity retention of 89.7% after 5000 GCD cycles at 20 mA cm −2 ). Asymmetric supercapacitor, assembled with CoFe 2 O 4 /Ni foam and activated carbon (AC) as positive and negative electrodes, respectively, exhibits high energy density of 6.01 W h m −2 at energy density of 50 W m −2 , indicating the promising application prospect of CoFe 2 O 4 /Ni foam in energy storage.

Quenching-induced surface modulation of perovskite oxides to boost catalytic oxidation activity

Quenching is a powerful method for modulating surface structures of metal oxide nanocatalysts to achieve high catalytic oxidation activities, but it is still challenging. Herein, a catalyst of ultrafine Co3O4 nanoparticles decorated on Co-doped LaMnO3 (Co3O4/LaCoxMn1−xO3) is synthesized via one-step quenching perovskite-type LaMnO3 nanocatalyst into an aqueous solution of cobalt nitrate, which exhibits significantly improved catalytic performance with toluene (1000 ppm) conversion of 90% at 269 °C under the gas hourly space velocity of 72000 mL g−1 h−1. The high catalytic activity correlates with large surface area, abundant oxygen vacancies and good reducibility. Furthermore, density functional theory calculations disclose that Co doping and interfacial effect of Co3O4/LaCoxMn1−xO3 can achieve lower C−H bond activation energy. These findings provide a unique and effective route towards surface modification of nanocatalysts.

Терапевтический эффект наноалмазов взрывного синтеза при кобальтиндуцированном дерматите

The aim of the research. To evaluate the therapeutic eff ect of modifi ed nanodiamonds (MND) of explosive synthesis for treatment of allergic contact dermatitis induced by cobalt ions. Material and methods. Th e study was performed on guinea pigs. Th e animals were divided into 3 groups (6 animals in each group). Allergic contact dermatitis was initiated using 2% aqueous solution of cobalt nitrate applied to the animals’ skin for 14 days according to the common procedure. For allergic contact dermatitis treatment, glycerol and MND suspension with the nanoparticle concentration of 5g · l-1 prepared in glycerol were used. MND with high colloidal stability in water suspensions and the average nanoparticle cluster size of d50 = 50nm was used in the work. Th e animals of group I were controls: aft er allergic contact dermatitis development, their skin was not treated by any means for 7 days. Th e animals in groups II and III were experimental: aft er allergic contact dermatitis initiation, their skin was treated for 7 days using glycerol and MND suspension, respectively. Upon experiment completion, biopsy of skin sample was performed on all animals for histological and spectral examination. The content of cobalt in skin samples was determined through atomic adsorption spectroscopy. Results. The results of histological and morphometric analysis indicate that, in the case with dermatitis modelled in guinea pigs using cobalt ions, treatment of the animals’ skin with MND suspension reduces allergic inflammation intensity. Th e therapeutic effect of MND is caused by adsorption of cobalt ions onto nanoparticles and their subsequent elimination from the skin, which complies with the atomic adsorption spectroscopy data. Conclusion. Th e prospects of MND as a new therapeutic agent for binding and elimination of chemical allergens (particularly, cobalt ions inducing the allergic contact dermatitis development) are discussed.

The facile conversion of iron foam into copper-coated 3D porous cobalt ferrite/iron foam for high-performance asymmetric hybrid supercapacitor

In this work, copper-coated CoFe2O4/iron foam (Cu@CoFe2O4/Fe) is synthesized with a facile method, including the growth of the copper film on the surface of iron foam via a displacement reaction between iron foam and Cu(II), and the subsequent partial conversion of the interior iron to CoFe2O4via a hydrothermal reaction by heating the copper-coated iron foam (Cu@Fe) in the aqueous solution of cobalt nitrate. Iron foam is used as the self-sacrificial template not only for the synthesis of cobalt ferrite foam but also the synthesis of the copper film. The high porosity of Cu@CoFe2O4/Fe facilitates the mass and charge transport at the solution/electrode interface, while the coating of the CoFe2O4 with copper film effectively hinders the volume expansion of CoFe2O4 and subsequently prevents the falling off of CoFe2O4 during the vigorous charging/discharging process, as evidenced by the high areal capacity, good rate capacity and extraordinary cycling stability of Cu@CoFe2O4/Fe.

Benzoic acid-assisted substrate-free synthesis of ultrathin nanosheets assembled two-dimensional porous Co3O4 thin sheets with 3D hierarchical micro-/nano-structures and enhanced performance as battery-type materials for supercapacitors

Two-dimensional (2D) porous materials have been proved to be meritorious for supercapacitors (SCs) due to unique properties of large surface area, superior intrinsic porosity and high electrical conductivity. In this work, we reported for the first synthesis of 2D porous Co3O4 thin sheets assembled by ultrathin nanosheets via direct hydrothermal decomposition of aqueous solution of cobalt nitrate in the presence of benzoic acid (BA) without any template or surfactant. High specific capacity (497, 598.5 and 399 C g−1 at 1.0 A g−1) and remarkable cycling stability (9.8, 6.3 and 13.1% loss over 8000 cycles at 10.0 A g−1) were achieved in a three-electrode system for the Co3O4 thin sheets at 200 °C for 6, 12 and 24 h with different specific surface area of 69.96, 142.15 and 42.07 m2 g−1, which can be attributed to the special structural feature of an open and porous surface layer and the synergistic effect of 2D and 3D structure that significantly facilitates fast electron transport, ion diffusion and intimate electrode/electrolyte contact. Furthermore, an assembled asymmetric supercapacitor (ASC, Co3O4 thin sheets//activated carbon (AC)) can reach a working output potential difference of 0–1.6 V with a maximum energy density of 22.49 Wh·kg−1 at the power density of 800 W kg−1 with excellent cyclic stability (only 8.2% loss of its initial specific capacity value over 10000 cycles). The results show that our synthesis provides a new insight into the fabrication of 2D hierarchical porous Co3O4 thin sheets; in addition, the as-synthesized Co3O4 thin sheets have potential for various applications in SCs, electrochemical sensing, and lithium ion battery.

Direct Synthesis of the Reduced Co–C/SiO2 As an Efficient Catalyst for Fischer–Tropsch Synthesis

The coimpregnation of the glucose and cobalt nitrate aqueous solution into SiO2 followed by the carbonization in an inert gas was demonstrated for the preparation of the directly reduced Co-xC/SiO2 (x: glucose to SiO2 mass ratio) Fischer–Tropsch (FT) catalysts. The as-prepared Co-xC/SiO2 (x = 0.1, 0.5, 1.0, 1.5) without any pretreatment was evaluated for FT synthesis under typical conditions. Significantly, the completely reduced Co-xC/SiO2 were obtained when the x was at or above 1.0, and the maximum normalized FT activity (cobalt-time-yield, CTY) of 3.5 × 10–4 molCO·g–1Co·s–1 over Co-1C/SiO2 was doubled the activity of the high-temperature reduced Co/SiO2. Moreover, light hydrocarbons (C1 ∼ C4) were favorably formed over Co-xC/SiO2, and the product distribution can be regulated via simply changing the ratio of the glucose to SiO2. The simple procedure and the cheap glucose make the directly reduced Co-xC/SiO2 catalysts very promising for the development of a more efficient FT process.

Cobalt-containing BEA zeolite for catalytic combustion of toluene

Co-containing HAlBEA zeolite was obtained by conventional wet impregnation of HAlBEA zeolite with an aqueous Co(NO3)2.6H2O solution, whereas Co-containing SiBEA zeolites were prepared by a two-step post-synthesis method. This approach consists of, in the first step, dealumination of parent BEA zeolite to obtain an aluminium-free SiBEA support and then, in the subsequent step, contact of the obtained material with an aqueous solution of cobalt nitrate. As shown by X-ray diffraction and low-temperature N2 adsorption, the dealumination of BEA zeolite and introduction of cobalt ions did not involve destruction of zeolite structure, and only insignificant blocking of pore system was observed after introduction of high amounts of cobalt. Nevertheless, clear changes in acidity were found by FTIR of pre-adsorbed pyridine after dealumination of parent BEA zeolite and introduction of cobalt ions. The presence of Lewis acid sites resulted in enhanced selectivity to CO and benzene formed as by-products in the toluene combustion. Therefore, SiBEA zeolite was chosen as a support for an introduction of various amounts of Co into the zeolite structure (the intended Co contents of 3.0–9.0wt%). Depended on the amount of the introduced Co, cobalt was incorporated into the framework of BEA zeolite as isolated mononuclear Co(II) species, small Co(II) oxide clusters and/or Co3O4 crystallites distributed in the whole zeolite structure. The chemical environment and dispersion of cobalt species were studied by transmission electron microscopy (TEM), FTIR of pre-adsorbed NO, UV–vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy (XPS). Temperature-programmed reduction of hydrogen (H2-TPR) was also performed to determine reducibility of the Co-containing SiBEA zeolites. It was confirmed that siliceous SiBEA zeolite was the excellent support of Co3O4, which was in turn recognized as the main active phase in the total oxidation of toluene. The best catalytic performance was achieved over the catalysts containing at least 0.05mmol of Co in the form of Co3O4 per 1g of SiBEA zeolite.

Modification of mesoporous alumina as a support for cobalt-based catalyst in Fischer-Tropsch synthesis

The high surface area, large pore volume and pore diameter mesoporous alumina was synthesized using pluronic F127 as a structure-directing agent. This material was employed as a support for the cobalt catalyst in Fischer-Tropsch Synthesis (FTS). During the catalyst synthesis, impregnation of cobalt nitrate aqueous solution caused a collapse in the structure and a drastic decline in the textural properties of the mesoporous alumina. Organic solvents such as acetone and ethanol were employed instead to realize their impact on the corresponding cobalt catalysts stability. The synthesized catalysts were characterized using BET, XRD, TEM, TPR, and H2 chemisorption. The catalysts prepared using organic solvents were found to retain the textural properties of the mesoporous alumina. The process conditions including temperature, pressure, and GHSV were optimized adopting Taghuchi experimental design. Then, all catalysts were tested in FTS utilizing syngas with H2/CO ratio 2.0, at optimized conditions of 230°C, 400psi, and GHSV of 900h−1. The Co/γ-Al2O3 catalyst was also synthesized and tested in FTS for the comparison study. The physico-chemical properties of the synthesized catalysts were correlated with their performances in FTS. The mesoporous alumina supported cobalt catalyst using ethanol as a solvent in its preparation was found to be the most stable in the series and it showed 8.3% higher CO conversion, 3.3% higher C5+ selectivity, and 2.7% lower CH4 selectivity as compared to those shown by Co/γ-Al2O3 catalyst. Higher cobalt loadings of 22.5 and 30wt% were also prepared using ethanol solvent and examined in FTS. Doubling the cobalt content from 15 to 30wt% of the catalyst resulted in stable catalyst with 23% increase in the hydrocarbon yield and 4% improve in C5+ selectivity.

Controlled Fabrication of Hierarchically Structured Nitrogen‐Doped Carbon Nanotubes as a Highly Active Bifunctional Oxygen Electrocatalyst

Hierarchically structured nitrogen‐doped carbon nanotube (NCNT) composites, with copper (Cu) nanoparticles embedded uniformly within the nanotube walls and cobalt oxide (CoxOy) nanoparticles decorated on the nanotube surfaces, are fabricated via a combinational process. This process involves the growth of Cu embedded CNTs by low‐ and high‐temperature chemical vapor deposition, post‐treatment with ammonia for nitrogen doping of these CNTs, precipitation‐assisted separation of NCNTs from cobalt nitrate aqueous solution, and finally thermal annealing for CoxOy decoration. Theoretical calculations show that interaction of Cu nanoparticles with CNT walls can effectively decrease the work function of CNT surfaces and improve adsorption of hydroxyl ions onto the CNT surfaces. Thus, the activities of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are significantly enhanced. Because of this benefit, further nitrogen doping, and synergistic coupling between CoxOy and NCNTs, Cu@NCNT/CoxOy composites exhibit ORR activity comparable to that of commercial Pt/C catalysts and high OER activity (outperforming that of IrO2 catalysts). More importantly, the composites display superior long‐term stability for both ORR and OER. This simple but general synthesis protocol can be extended to design and synthesis of other metal/metal oxide systems for fabrication of high‐performance carbon‐based electrocatalysts with multifunctional catalytic activities.

Influence of the nature and environment of cobalt on the catalytic activity of Co-BEA zeolites in selective catalytic reduction of NO with ammonia

The influence of cobalt environment on the catalytic properties of CoxSiBEA zeolite in selective catalytic reduction of NO with ammonia was studied. Catalysts were prepared by a two-step postsynthesis method which consists, in the first step, of dealumination of parent BEA zeolite to obtain aluminum-free SiBEA support and then, in the second step, of contacting the obtained material with an aqueous solution of cobalt nitrate. DR UV–Vis and XPS results showed that cobalt was successfully incorporated into zeolite beta framework as isolated mononuclear Co(II). The presence of only isolated framework mononuclear Co(II) was evidenced in CoxSiBEA with cobalt content lower than 2 wt % and both isolated framework mononuclear Co(II) and extra-framework octahedral Co(II) for Co3.0SiBEA catalyst. FTIR investigation of pyridine adsorption revealed that the incorporation of cobalt into zeolite framework led to a creation of new Lewis acidic sites which are responsible for high activity in SCR of NO with ammonia. The catalytic activity of CoxSiBEA in selective catalytic reduction of NO with ammonia as reducing agent strongly depends on the nature and environment of cobalt in BEA structure. The single-site Co2.0SiBEA zeolite catalyst was the most active among tested, with maximum NO conversion about 80% at 673 K. In contrast, Co3.0SiBEA catalyst containing a mixture of framework and extra-framework Co(II) had lower activity in SCR of NO process than Co2.0SiBEA at higher temperature due to a competitive reaction of ammonia oxidation to NO.

Enabling visible-light water photooxidation by coordinative incorporation of Co(II/III) cocatalytic sites into organic-inorganic hybrids: quantum chemical modeling and photoelectrochemical performance

Coordinative incorporation of Co(II/III) cocatalytic sites into organic–inorganic hybrids of TiO2 and “polyheptazine” (PH, poly(aminoimino)heptazine, melon, or “graphitic carbon nitride”) has been investigated both by quantum chemical calculations and experimental techniques. Specifically, density-functional theory (DFT) calculations (PBE/def2-TZVPP) suggest that Co(II/III) and Zn(II) ions adsorb in nanocavities at the surface of the hybrid PH–TiO2 cluster, a prediction which can be further confirmed experimentally by 15N nuclear magnetic resonance in the case of the Zn complex. The absorption spectra of the complexes were characterized by time-dependent DFT calculations, suggesting a change of color upon Co ion binding which can in fact be observed with the naked eye. Hybrid TiO2–PH photoelectrodes were impregnated with Co(II) ions from aqueous cobalt nitrate solutions. Optical absorption data suggest that Co(II) ions are predominantly present as single ions coordinated within the nitrogen cavities of TiO2–PH, and any undesired blocking of light absorption is negligible. The cobalt-induced cocatalytic sites can efficiently couple to the holes photogenerated by visible light in TiO2–PH, leading to complete oxidation of water to dioxygen. Our results indicate that coordinative incorporation of metal ions into well-designed surface sites in the light absorber is sufficient to drive complex multielectron transformations in artificial photosynthetic systems.

Effect of preparation method of Co-promoted Pd/alumina for methane combustion

Effect of preparation method of Co-promoted Pd/alumina for methane combustion was investigated. The addition of Co was carried out by two methods: co-impregnation of an aqueous solution of palladium nitrate and cobalt nitrate mixture, and sequential impregnation of an aqueous solution of cobalt nitrate to Pd/alumina. At the loading amount of 1–3wt%, the co-impregnated catalysts showed the higher activity than un-promoted Pd/alumina, while the sequentially impregnated catalysts showed the lower activity. XPS and IR spectra of adsorbed CO indicated that the oxidation state of Pd was not much affected by the preparation methods. Good dispersion of Co on the co-impregnated catalyst was demonstrated by HAADF-STEM images, while less interaction between Co and Pd was suggested on the sequentially impregnated catalysts. The profiles of temperature programmed reduction by methane indicated that the better dispersion of Co on Pd resulted in the better reducibility of Pd species, which is attributed to the higher methane oxidation activity of co-impregnated catalysts.

Preferential chemical vapor deposition of ruthenium on cobalt with highly enhanced activity and selectivity for Fischer–Tropsch synthesis

Various amount of ruthenium was preferentially deposited on cobalt of Co/γ-Al2O3 by chemical vapor deposition (CVD) of ruthenocene and compared with a CoRu/γ-Al2O3 catalyst prepared by the usual impregnation method for Fischer–Tropsch synthesis (FTS). The Co/γ-Al2O3 was prepared by wet impregnation of cobalt nitrate aqueous solution, and then dried and calcined at 400°C for 4h. Ruthenocene was sublimated, carried by argon, and then mixed with H2 and passed over γ-Al2O3 or calcined Co3O4/γ-Al2O3 catalyst at various temperatures. The effluent gasses were passed through a gas cell of FTIR to determine the ruthenocene thermo-chemical decomposition products. In a temperature range (window) of 150–200°C the ruthenocene decomposes on Co3O4/γ-Al2O3 but not on γ-Al2O3. The catalysts were characterized by TPR, EDX, TEM, XRD and BET. The FTS activity and selectivity of the Ru-Co/γ-Al2O3 catalysts were investigated in a fixed bed microreactor. The preferential CVD of 0.3wt% ruthenium onto 15.0wt% Co/γ-Al2O3 (CoRu5-180) catalyst shifted both cobalt TPR peaks by about 120°C to lower temperatures, showed about 2.8 times higher conversion, 30% more C5+ selectivity, and 30% less selectivity of methane. The CoRu5-180 catalyst showed about 81% higher CO conversion and 12% higher selectivity to C5+ than the same catalyst composition prepared by the used impregnation of ruthenium chloride onto the 15.0wt% Co/γ-Al2O3.

COBALT SUPPORTED ON ZSM-5 ZEOLITE USING KAOLIN AS SILICON AND ALUMINUN SOURCES FOR FISCHER-TROPSCH SYNTHESIS

The use of clay as an alternative source of raw material provides economic routes for the synthesis of ZSM-5. Therefore, the main purpose of this work was to study ZSM-5 synthesis using kaolin as Si and Al source. The zeolite using kaolin as a source of silica and aluminum has been applied as support for a 20wt% Co catalyst. Zeolite ZSM-5 was obtained with kaolin under hydrothermal synthesis at 373K for 48 hours. The kaolin was submitted to heat treatment at 973K for 2 hours before being used in synthesis. The deposition of cobalt on the support ZSM-5CK was performed by means of wet impregnation, using a 0.1-M aqueous solution of cobalt nitrate. The catalytic support and metal-loaded catalyst have been characterized and evaluated for the Fischer-Tropsch Synthesis (FTS) under controlled conditions (T = 593K, P = 20atm, H2:CO molar ratio = 2) in a fixed bed reactor for 150 hours. From the Temperature Programmed Reduction profiles, two reduction peaks were observed at 629K and 677K, corresponding to the stepwise reduction of Co3O4 particles to CoO and then to metallic Co on the support external surface. It was observed with the FTS results that the 20wt% Co/ZSM-5CK catalyst yielded a 10% conversion rate and high selectivity towards the production of C5+ (98%).

Preparation, characterization and photocatalytic activity of Co3O4/LiNbO3 composite

Abstract The Co3O4/LiNbO3 composites were synthesized by impregnation of LiNbO3 in an aqueous solution of cobalt nitrate and next by calcination at 400°C. The activity of produced samples has been investigated in the reaction of photocatalytic hydrogen generation. The crystallographic phases, optical and vibronic properties were studied using X-ray diffraction (XRD), diffuse reflectance (DR) UV-vis and resonance Raman spectroscopic techniques, respectively. The influence of cobalt content (range from 0.5 wt.% to 4 wt.%) on the photocatalytic activity of Co3O4/LiNbO3 composites for photocatalytic hydrogen generation has been investigated. Co3O4/LiNbO3 composites exhibited higher than LiNbO3 photocatalytic activity for hydrogen generation. The highest H2 evolution efficiency was observed for Co3O4/LiNbO3 composite with 3 wt.% cobalt content. The amount of H2 obtained in the presence of LiNbO3 and Co3O4/LiNbO3 (3 wt.% of cobalt content) was 1.38 µmol/min and 2.59 µmol min−1, respectively.

Synthesis of Catalysts and Its Application for Low-Temperature CO Oxidation

A series of Au/-TiO2 with various Co/Ti ratios prepared. /TiO2 was prepared by incipient wetness impregnation with aqueous solution of cobalt nitrate. Au catalysts were prepared by deposition-precipitation (DP) method at pH 7 and 338 K. The catalysts were characterized by inductively coupled plasma-mass spectrometry, temperature programming reduction, X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The reaction was carried out in a fixed bed reactor with a feed containing 1% CO in air at weight hourly space velocities of 120,000 mL/h g and 180,000 mL/h g. High gold dispersion and narrow particle size distribution were obtained by DP method. The addition of into Au/TiO2 enhanced the activity of CO oxidation significantly. Au/5% -TiO2 had the highest catalyst among all the catalysts. was mainly in the form of nanosize Co3O4 which could stabilize the Au nanoparticles. donated partial electrons to Au. The interactions among Au, , and TiO2 account for the high catalytic activity for CO oxidation.

Effect of bimodal porous silica on particle size and reducibility of cobalt oxide

In this study, the effect of bimodal porous silica (BPS) on particle size and reducibility of cobalt oxide has been investigated. Unimodal porous silica (UPS) was used for comparison purposes. Both silica supports were impregnated with an aqueous solution of cobalt nitrate to obtain cobalt loadings of about 10 wt%. Pore structure, specific surface area, morphology and cobalt oxide crystallite size of the cobalt oxide loaded on porous silicas were systematically characterized by means of N2-sorption, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The reduction behavior profiles and the activation energy for the reducibility of the cobalt oxide were studied by dynamic thermal gravimetric under flow of H2. The average particle size of cobalt oxide loaded on the BPS sample was revealed to be slightly larger than that loaded on the UPS sample, likely because cobalt oxide particles were distributed both on mesopores and macropores. The reduction temperatures of the cobalt oxide loaded on the BPS sample were found to be evidentially lower than those of the cobalt oxide loaded on the UPS sample.

CO2 hydrogenation over Co/Al2O3 catalysts prepared via a solid-state reaction of fine gibbsite and cobalt precursors

The properties of Co/Al2O3 catalysts prepared by the solid-state reaction between gibbsite and various cobalt salts such as cobalt acetate (CoAc), cobalt acetylacetonate, cobalt chloride, and cobalt nitrate (CoNT) were investigated in the hydrogenation of carbon dioxide at 270 °C and atmospheric pressure and characterized by N2 physisorption, X-ray diffraction, X-ray photoelectron spectroscopy, and H2-temperature programmed reduction. Compared to the catalyst prepared by conventional impregnation of aqueous solution of cobalt nitrate on alumina (CoNT-Imp), the solid-state catalysts (CoNT and CoAc) exhibited much higher activity in the CO2 hydrogenation with comparable CH4 and CO selectivity. Unlike the impregnation catalysts, in which most of the Co3O4 particles/clusters were located deep inside the pores of alumina, the solid-state reaction resulted in the dispersion of cobalt oxides mostly on the external surface of alumina. As a consequence, CO2 adsorption and dissociation to adsorbed CO and O (the initial steps in CO2 hydrogenation) were not limited by the slow diffusion of CO2 so high CO2 hydrogenation activity was obtained. As revealed by the XRD and H2-TPR results, the average crystallite size of Co3O4 and the metal-support interaction depended on the cobalt precursor used during the solid-state synthesis. Nevertheless, the solid-state reaction of gibbsite and cobalt chloride at 650 °C resulted in very poor CO2 hydrogenation activity due to the formation of inactive cobalt aluminate.

FISCHER-TROPSCH SYNTHESIS IN SLURRY-PHASE REACTORS USING Co/SBA-15 CATALYSTS

The objective of this work is to describe the production of bifunctional catalysts using the incipient humidity method, producing catalysts with 15 wt.% cobalt supported in SBA-15 molecular sieve, to be applied in the Fischer-Tropsch (FT) reaction. The originality of this work is its focus on the use of a 15 wt.% Co/SBA-15 catalyst in FT synthesis in slurry reactors. The deposition of cobalt over SBA-15 support was accomplished by impregnation with a 0.1-M aqueous solution of cobalt nitrate. The Fischer-Tropsch synthesis was carried out with the catalyst at 240 °C and 20 atm, under a COH2 atmosphere (molar ratio= 1), in a slurry reactor for 8 hours. X-ray diffraction measurements showed that the calcined cobalt catalyst did not modify the structure of SBA-15, proving that Co was present under the form of Co3O4 in the catalyst. The addition of cobalt in the SBA-15 decreased the specific superficial area of the molecular sieve. The 15 wt.% Co/SBA-15 catalyst had a 40% CO conversion rate and a high selectivity towards the production of C5+ (53.9% after 8 hours).

Study of the effect of cobalt content in obtaining olefins and paraffins using the Fischer-Tropsch reaction

This work presents the synthesis, characterization and testing of catalysts for the Fischer-Tropsch reaction. Molecular sieve MCM-41 was prepared under hydrothermal treatment at 150°C for 2 days, using the following molar composition of reagents: 1 SiO2:0.27 CTABr:0.19 TMAOH:40 H2O. Obtaining the mesoporous molecular sieve, Si-MCM-41, was confirmed by X-ray diffraction. The deposition of cobalt on MCM-41 support was carried out by wet impregnation, using an aqueous solution of cobalt nitrate. The images obtained from TEM clearly showed a good dispersion of the cobalt on the support (MCM-41). The textural characteristics of the samples were investigated by isothermal gas adsorption/desorption. Using the BJH method, it was possible to obtain the values of the average pore diameter on adsorption and desorption. The obtained catalysts containing different cobalt concentrations were evaluated for the Fischer-Tropsch reaction. Increasing the temperature increases the selectivity to olefins with the 15wt.% Co/MCM-41 catalyst, as well as increases the selectivity to methane with the 5wt.% Co/MCM-41 catalyst.